Consul

Legiones Consularis, or Consuls, were a set of specialist ranks bestowed upon veteran Space Marines during the Great Crusade and Horus Heresy. They should not be confused with Legion Consuls, who were basically the military police of the Legions. They were identified by their specialization in given areas of warmaking. Called upon to use their mastery when their Legion needed them, with the outbreak of the Horus Heresy these officers would face their grandest trial. As one can imagine, there is a metric shit-tonne of different variants of Consuls.

Variants

Armistos

Where the Champion is a master of blades, the Armistos is a master of firepower, the bigger the better. Usually assisted by masters of the armory, the Armistos was constantly testing the most cutting-edge firearms in order to find the finest means to deliver death from afar.

In the Horus Heresy tabletop, the Armistos gains hardened armour to protect themselves from blasts as well as a Cognis Signum. Most notably, they gain access to an array of master-crafted heavy weapons, allowing them to run around and blow shit up more efficiently.

Castellan

The Castellans of the VII Legion were relentless in drilling their troops to perfection in marksmanship. When they left a newly conquered world, they left behind a new set of fortifications, staffed by loyal soldiers.

The Castellans are an VII Legion-exclusive addition to the Liber Astartes in the 2nd edition of the Horus Heresy tabletop. Similar to the Armistos, they get hardened armour and a master-crafted heavy weapon - though their options are restricted to the heavy bolter, autocannon, and the legion-exclusive Iliastus Assault Cannon. They're one of the shootiest characters in the current edition and can be absolutely trolltastic with the right setup.

Champion

The predecessor to the Company and Chapter Champions of the Chapters, their role has seen the least amount of change. After all, the Champion was always meant to be an exemplary swordsman among their brothers and fight the greatest foes. How else were they to improve that?

Chaplain

While the Imperial Cult was not established yet, the Legiones Astartes still had room in their order of battle for dudes who shouted really loudly at them about the need to kill xenos scum for great justice. Similar to their successors in black and bone, these Chaplains would inspire hatred in their charges and wield a master-crafted Power Weapon - though unlike the Crozius Arcanum synonymous with the later iterations, these could be any sort of power weapons than merely mauls.

Speaker of the Dead

Before the VI Legion had Wolf Priests mixing Fenrisian lore with the Imperial Creed, the Speakers of the Dead were the resident Apothecaries-slash-cult leaders of the lesser deity Morkai.

In the tabletop, this not only gave an attached unit Hatred (Everything) and Stubborn, but they also gained a Narthecium and a master-crafted power maul in place of the Crozius.

Delegatus

In smaller conflicts where the Legion's senior command did not see the need to directly intervene, they would deputize a lesser officer, typically a Centurion, with full command of their own army. These officers would then assemble their own strike forces to lead into battle.

In the tabletop game, the Delegatus is an upgrade that offers no special equipment, but it does grant the Consul the Master of the Legion rule, and thus the ability to qualify as the warlord in smaller games as well as the ability to select a Rite of War as if they were a Praetor. They also get a single-use ability to roll a Leadership Check to force any units that were falling back or pinned to rally and act normally for the turn.

Forge Lord

Though trained on Mars in the ways of the Mechanicum, unlike the Praevians the Forge Lords were selected for their incredible skill with machinery. While they made use of the war machines of the Mechanicum, their real job was repairing the Legion's armoured forces. As with their successors, these Forge Lords were usually in charge of overseeing supply and weapons production for the Legion.

On the Horus Heresy tabletop, Forge Lords have servo-harnesses to help them repair their vehicles as well as being useful multi-weapons. On top of this, they can also purchase Cortex Controllers, which prove particularly useful if they decide to ally with any automata on the field, including the Thallax maniples that they unlock access to.

Herald

The forebears of the Chapter and Company Ancient, the Herald is charged with holding carrying their Legion's standard into battle. As ever, the Legions fought with religious fervour to protect those who held these artefacts, which were usually touched by the Primarch and gifted to an officer as a sign of favor.

The tabletop represents Heralds by forcing them to sacrifice either their pistol, bolter, or combi-bolter so they have a free hand to hold this weighty standard.

Librarian

Due to the Council of Nikaea, the Librarius was dissolved among the legions, but as many can attest, this was not for long.

In most cases, a psyker was elevated to a more senior position to make use of their unnatural powers, but as time passed, it became clear that the powers of psykers were one of the only ways to defeat the foul warpspawn that the traitors summoned...or to summon them. Following the Heresy, Guilliman would formally reestablish the Librarius as a structure in the Chapters.

As with their successors, these Librarians have access to Force Weapons with which to channel their psychic powers. Psychic Hoods did exist in this era in order to help cancel out any harmful psychic influences, but they were not so common that they could be issued to any Librarian that wanted one.

Caster of Runes

Before they were called Rune Priests, the Casters of Runes were the standing psychic force of the VI Legion. Of course, they were deemed "exceptions" to the ban on Librarians due to claiming their powers were derived from shamanism and channeling the spirit of their homeworld of Fenris. Nobody bothered to call them out on this due to the fact that the Space Wolves were effectively the Emperor's attack dogs that got sicced on any naysayers.

Practically, aside from their limited choice in psychic powers (including some of their own), they were identical to Librarians.

Esoterist

Among the psykers of the legions, only a few dared to dive deep into the unknown fields of Warpcraft, but it proved to be incredibly effective, if in varying ways. While the loyalist legions had Esoterists who studied how to banish daemons outright, the traitor legions discovered ways with which they could summon the forces of Neverborn into reality with their own power.

Esoterists are a specialization that were originally introduced at the tail end of the first edition of the HH tabletop. They are identical to Librarians with two exceptions - one is access to Archaeotech Pistols, but the bigger one is their unique Anathemata psychic discipline (or the Sanctic/Malefic Daemonology in the original books), which normal Librarians don't get access to.

Stormseer

Similar to the VI Legion, the Stormseers of the V Legion were also treated as special "exceptions" to the no-Librarians rule due to being shamans, though the Stormseers weren't so hypocritical as to reject the Librarius as a failed structure. These Stormseers would persist after the Heresy and effectively become the Librarius for the chapter.

Practically, aside from their limited choice in psychic powers (including some of their own), they were identical to Librarians.

Diabolist

Is it any surprise that these consuls hailed from the XVII Legion? Indeed, as Lorgar dove further into the Primordial Truth, so too did his sons continue diving into this forbidden lore of the daemons, even as this knowledge corrupted their souls and twisted them. One might assume them as the predecessor to the Master of Possession that would lead the Legions of Chaos, and that is quite close a guess.

In the Horus Heresy tabletop, these consuls are special psykers with force weapons who partake in forbidden daemonology, essentially becoming daemons. This will require the rest of the army to take Dark Channeling to similarly become daemons if you want the Diabolist to join a squad. Unlike the Librarian, they see no need for a psychic hood since summoning daemons to fuck shit sideways is the whole point of what they're doing.

Moritat

Though the role of Consul was typically an honoured one, the Moritat received no such acclaim. Being drawn from the oft-scorned Destroyer companies, the Moritat was specially tasked to deliver death on their own, operating outside the Legion's normal command structure as a one-man special forces squad.

On the Horus Heresy tabletop, the Moritat is notable for their ability to take rad grenades and their dual-pistol loadout. The latter is their most iconic feature as it lets them rapid fire these pistols to an almost comical degree. However, the Moritat is also unable to lead anything aside from an attached Destroyer squad.

Mortificator

Among the ranks of the Techmarines, the Mortificators are those who spend the most time with the honoured Dreadnoughts of the legion. As they know the most about these venerated war machines, they will accompany the dreads into the fray, constantly ensuring that they operate at their finest.

On the Horus Heresy Tabletop, the Mortificator serves as the keeper of the dreads. He can be attached to a Dreadnought talon, in which case the dreads gain a Feel No Pain save on top of the consul's ability to repair them. The Mortificator comes equipped with a servo-arm and a Corposant Stave, an unusual archaeotech weapon that can overload enemy machinery.

Pathfinder

With the extreme demand for frontline troops in the Heresy, there were few scout companies that were utilized as they tended to be thrown into power armour as soon as possible. As a result, the scouts of these days tended to be experts in the field, opting for light armour for the sake of completing covert ops that the rest of the legion would not see as feasible.

In the Horus Heresy tabletop, the Pathfinder is an addition to the Liber Astartes/Hereticus books of the second edition. The Pathfinder is the only Consul equipped with Scout Armour, but for some reason he doesn't gain the Light sub-type.

Praevian

In the Great Crusade, Battlebots were an actual thing.

The Consul Praevian was a type of Astartes commander during the Great Crusade and Horus Heresy and a variant of the Consul.

Trained on Mars by the Mechanicum, Praevians were the keeper of the Legion's robots, including Battle-Automata given honorary induction into the Legion's ranks. On the field of battle they marched at the forefront of Battle-Automata forces, guiding them through the engagement.

They were often chosen from veterans whose injuries required extensive bionic replacement. Known to be solitary individuals, they rarely advanced up the chain of command. Some Legions used the rank as a dumping ground for warriors seen as unfit for other duties. However, in the Iron Hands (No surprise there) and Salamanders, the rank was seen as a great honour. On the traitor side, Iron Warriors also make great use of them due to their ability to bring siege robots to the party. As they are heavily augmented, they wore what is essentially Artificer Armour for defence, but by the time of Horus' clusterfuck bonanza some of them had to wear Heresy-pattern armour.

Some people call them a predecessor of the Techmarine, but with each of them in command of a mini robot-army.

On the tabletop, they are the Master of the Legion's Automata. The Praevian is a Support Officer, so cannot be used as a compulsory HQ and thus cannot be in an allied contingent. Comes equipped with a Cortex Controller, Cortex Designator and can't take anything that makes him bulky. First, you choose a type of Battle Automata (only Castellax and Vorax at this time) to accompany him, forming one unit with MCs (so he can't go to ground) that he can't leave. Any time the Praevian hits an enemy unit with a ranged attack, he grants Preferred Enemy to the Automata in his unit for that turn (so give him a bolter). Upgrade them with Enhanced Targeting Arrays for 2+ re-rollable accuracy for your weapons.

In the first edition, Praevians were unique in that they not only treated their charges as members of the legion, but they could also equip them with special equipment that might have proved useful to them.

Primus Medicae

Chosen from the most senior officers of the Apothecarion, the Primus Medicae was the figure in charge of the well-being of his brothers and their gene-seed. In those situations where they take to the field, the Primus Medicae is singularly dedicated to the safety of the Legion's health.

On the tabletop, the Primus Medicae has a Narthecium, as befits their station, as well as a special rule to let an attached unit re-roll any Feel No Pain saves they make from that Narthecium. re-roll IWND rolls. Who the fuck wrote that? At least this makes him good at buffing Primarc-...wait, what do you mean he only lets Infantry and Cavalry re-roll IWND rolls?

At the very least he's the only Narthecium carrier able to take Terminator armour, so has a niche as the Feel No Pain provider for your Deathstar.

Primus Nullificator

As the Heresy ground on, the loyalists tried a great many methods to ward off the hordes of daemons being summoned by the traitor forces. One of these would be Nullificators, a small force of marines who etched their power armour with hexagrammatic wards and used superstition and normally unsanctioned weapons like disintegrators. Primus Nullificators were the leaders of these forces, psykers who were specially trained to purge daemons.

On the tabletop, the Primus Nullificator uses these Hexagrammatic Wards to protect themselves against the warp. Alongside their guns (which could also include the disintegrator), they wield the Aether-shock Maul, a special power weapon made to demolish daemons. Their main goal is opening extended access to the Nullificators, allowing one to field them without restriction as a Troops choice, though they're a Support Squad so they can't score objectives.

Siege Breaker

When there were fortifications or armored vehicles that needed to be gone yesterday, the Siege Breakers were the ones who got the call. Usually leading from the front, the Siege Breaker devoted himself to smashing the enemy's walls and trashing their tanks.

On the tabletop, the Siege Breaker comes loaded for bear, with a Nuncio-Vox to direct artillery strikes and Phosphex Bombs to scorch the earth. More importantly, they can give Sunder to a unit within 6" each turn and they unlock phosphex rounds for Rapiers and Arquitors, letting you bring creeping death to the field.

Dark Emissary

Agent of the Warmaster and the XVI Legion, the Dark Emissary was dispatched to other legions, seeking to corrupt their leadership by whispering honeyed words to those who would listen. Often, they would subvert the warrior lodges to make their work easier, spreading corruption and deceit through the lodges' clandestine gatherings. For those that turned from the Emperor, the Dark Emissary became the voice of their leader and enforcer of Horus' will.

The Dark Emissary is a Sons of Horus-exclusive consul in the HH tabletop. As they are not warlords, they are instead seen only in allied detachments of the Sons of Horus. They wield the Staff of Dark Authority, a special power weapon that serves as their badge of office.

Pack Thegn

Serving the Jarls of the VI Legion's great companies, the Thegns are champions of the Rout, with plenty of experience to impart to their troops. However, they do not view this as an honour, as these Thegns have been passed up for promotion as Jarl, whether by suffering some grave dishonour or as the lone survivor of their pack.

The Pack Thegn is a Space Wolves-exclusive Consul introduced in the Liber Astartes. They don't add much, giving only Counter-Attack (1) as well as the Skirmish unit sub-type, which lets them integrate with the legion's unique units without much trouble.

Paladin of the Hekatonystika

The I Legion was known for its labyrinthine web of orders, cabals, and chambers, an anomalous organization that made the Legion impenetrable to outsiders and allowed its commanders to draw upon the unique knowledge of each order as needed. Among these are the Hekatonystika, an order shrouded in extreme secrecy but uniquely experienced in a special art of warfare. A Paladin may on occasion be assigned from the orders of the Inner Circle to take the lead in a situation where the order's experience would prove absolutely necessary.

The Paladin of the Hekatonystika is a Dark Angels-exclusive consul introduced in the Liber Astartes of the HH tabletop reboot. He gets a Terranic Greatsword and can select one of the choices for the Orders of the Hekatonystika given to the Inner Circle Knights Cenobium. With the bump to Leadership and WS as well as Stubborn, the Paladin is basically an improved Consul Champion, though he's not honour-bound to accept any challenges.

Phoenix Champion

The Phoenix Guard are the most elite terminators of the III Legion, masters of combat and icons of Fulgrim's pride. The Phoenix Champion is the most elite of these guardians, acting as the shining exemplar of a legion that prides itself on outright perfection.

The Phoenix Champion is a unique consul introduced with the Liber Hereticus of the HH tabletop reboot. These consuls gain the same special rules as the Phoenix Guard as well as the exquisitely decorated and master-crafted Phoenix weapons the wielded.

Vigilator

The lone gunmen of the Legiones Astartes. Vigilators were highly trained snipers who typically embarked on infiltration, reconnaissance, sabotage, and decapitation missions behind enemy lines. Some Legions thought they were dishonourable and refused to incorporate them into their order of battle, but others, like the Alpha Legion and the Raven Guard, made excellent use of them.

On the tabletop they come equipped with a master-crafted Nemesis Bolter and get melta bombs for free. They have the option to be given either Infiltrate or Scout. They aren't Skirmish sub-type though, so they don't mix well with Recon Squads, which is a shame, but they do have the same Marked for Death special rule that Seekers do, so they can re-roll 1s to-wound against a single unit chosen at the start of the game. They also have the Master Sniper rule, which gives any Sniper weapon they use the Rending (2+) and Shell Shock (1) rules. So effectively against their chosen target with their Nemesis Bolter, they auto-hit (BS5 Master-crafted) and auto-wounding with AP2 (Rending (2+) and Marked for Death).

Saboteur

Saboteurs were an elite group of Alpha Legionnaires who were basically Vigilators if they focused exclusively on dicking over the enemy's army. After all, your opponent can't fight if his comms are jammed, his armor and artillery are wrecked, his commanders are dead, his troops are in the wrong spot, and his fortifications have been breached.

The Saboteur is an XX Legion-exclusive consul in the second edition of the Horus Heresy tabletop. He comes stock with Infiltrate and Scout, plus a rule known as False Colours that prevents him from being attacked until he attacks. He also gets melta bombs, breacher charges, and shroud bombs for free and can buy a Nemesis bolter for cheap because the Alpha Legion doesn't fuck around in the dirty-tricks department.

Warmonger

Junior captains who were eager to make a name for themselves, Warmongers specialized in close-assault tactics and deep striking via teleport, allowing them to get right up in the enemy's face before blowing it off. They fit better into some legions than into others.

Warmongers have been relegated to PDF status as of the second edition of the Heresy tabletop, which is probably fine since they're kind of a one-trick pony. They get an Aetheric Juncture Splicer, which allows them and an attached squad to deep-strike, so you could theoretically troll your opponent by dropping him and a Breacher squad onto an objective...but you have to roll a d6 when you deploy them and rolling a 1 deals an automatic wound. The Warmonger also has to charge whenever he can, which can be problematic if he's Leeroy-Jenkinsing a Terminator squad or a Dreadnought without proper kit.