Azrael
Azrael is the secretive Supreme Grand Master (Chapter Master) of the already secretive Dark Angels Chapter of Space Marines, not to mention the de facto Chapter Master of every single chapter with Lion El'Johnson's gene seed (basically the Dark Angels are guilty of legion-building).
History
Azrael was recruited from the brutes of Kimmeria, but does not show their clumsy-ass thuggish behaviors. He is best known within his chapter for caring for the banner, the scouring of Truan IX, and kicking the shit out of some techno-revivalist cult on Faze V. After that, he disappeared like Robert Pattinson's balls after Twilight. He must've got shit done over those few decades, because he was promoted to a member of the Deathwing, followed by Captain of the 3rd Company, and finally the Master of the Deathwing.
Azrael became the Chapter Master of the Dark Angels after the previous master's demise, becoming the head of the Inner Circle, the big boy table of the Dark Angels that keeps the secret of the Fallen Angels ABSOLUTE LOYALTY OF THE CHAPTER DURING THE HORUS HERESY. When he became Keeper of the Truth he received the traditional Lion's Helm (which, humorously, was called ridiculous by Kharn during the Pandorax Campaign, and which easily gave him away as Supreme Grand Master), the master-crafted Sword Of Secrets, and a combi-plasma gun known as the Lion's Wrath.
Recently, Azrael has been getting a lot more screen time from Black Library, particularly in recent fluff surrounding the Pandorax campaign, portraying him in an interestingly multi-faceted light, unlike most Chapter Masters who are the epitome of their chapter and often come across as one-dimensional. For instance, when dealing with the Grey Knights Azrael deals with them so casually he constantly pisses of Kaldor Draigo by cheekily misrepresenting his rank of Supreme Grand Master, he also snickers his way through the evil monologue of the daemon prince end-boss Corpulax before executing him. Furthermore Azrael does not allow a single battle-brother to suffer a mind wipe after fighting alongside the Grey Knights, as per norm operations. (Making Azrael less of a pussy than Dante who caved to that pressure, and more of a diplomat than Logan Grimnar who would generally RAGE against the Grey Knights instead)
Also, despite the Dark Angels sometimes coming off as emo dispassionate pricks, he is quite vocal about his support and admiration for allied Imperial Guard, and quickly warms to the personality of Catachan Colonel Strike when he starts telling Grey Knights what to do. By contrast though, Azrael can still be a douchebag and violently but efficiently turn on his allies whenever they are exposed to the Fallen. So in this regard, as least he's consistent with his chapter's priorities.
Tabletop
In-game Azrael is the Dark Angel's ubiquitous "costs as much as a Land Raider" HQ. He isn't all that bad and he gives an invulnerable save to the unit he joins, but he cannot take Terminator armor to thug it up with Terminators (that is Belial's job) or a bike (much less Sammael's LAST IMPERIAL JETBIKE). Overall, not a terrible unit but his place in the army is limited. With the changes to 6th, he is FAR more survivable in combat due to his Artificer Armor, but on the other hand his power sword is now only AP3. But the new DA codex gives him the ability to turn BOTH Deathwing and Ravenwing into troops, so it all works out quite nicely. If you take him in the primary detachment he must be the warlord, however you get to choose any trait from the DA's warlord table without rolling so its still cool. Taking him with guard allies lets you apply his helm of 4++ to a 50-man infantry blob to really ruin someone's day.
Trivia
- Azrael's name is fitting, as he is named after biblical Azrael, the Angel of Death (which is another name for the Space Marines).