Fabius Bile

Told you.

Unlike you, whelp, I once walked the same ground as your Idol. I breathed the same air as him. And I tell you this, without lie or artifice. He never wanted to become what you have made him! He did not wish to be your god-thing. He abhorred such ideals! The slavery of your crippled, blind Imperium would sicken him, if he had eyes to see it.
- Fabius Bile, telling it like it is to Rafen of the Blood Angels - Black Tide

"I was building another science, my science, wild science, robots and lasers and disembodied brains. A science that buzzed and glowed; it wanted to do things. It could get up and walk, fly, fight, sprout garish glowing creations in the remotest parts of the world, domes and towers and architectural fever dreams. And it was angry. It was mad science."
- Dr. Impossible - Soon I Will Be Invincible

Fabius Bile (Fabulous Bill or simply "Bob") is the mad scientist to end all mad scientists (since to the Haemonculi science comes second to pain). He's got a lab coat made of human skin and a pimpin' staff.

He is also absolutely fabulous BLAM! Heresy!!!.

He has the ability to hook up with a squad and pump them full of his pimp cane juice, making them get on board the Rape Train and head right for the front cabin. His pimp cane also causes Instant Death, though it counts as a regular weapon so he's likely to survive against anything decent armor (very bad given that counting the CSM codex, six the armories out right are MEQ, with the Necrons also being close behind). Put him in with a squad of Berserkers or Possessed who scored themselves power weapons and stuff them in a Land Raider. It's time to rev the Fun Bus the fuck up and have yourselves a party.

The Great Crusade

Fabius was the Chief Apothecary of the Emperor's Children. Before Fulgrim was rediscovered, the legion was afflicted by a degenerative geneseed flaw known as the Blight - a progressive form of cancer that caused random tumors in both bones and organs. Fabius was tasked with finding a cure, lest the flaw wipe out the Emperor's Children to a man. He gradually became more morose as his work only led to failure (as well as prompting his future experimental streak). All the Terran marines of the legion were susceptible to the disease and Fabius was forced to euthanize a lot of his friends and comrades, leading to him seeking solitude away from his battle brothers.

It turns out that a cure was never actually found, and that reuniting with their Primarch on Chemos (really GW? You literally put the cancer marines on chemo?) only served to provide fresh material for "untainted" space marines. All those who suffered the flaw were put to death in an attempt to prevent any infection from reaching the healthy brethren... Except for Fabius himself who was in a position to falsify his medical records. His prognosis was that he only had about a year to live, but had developed a process of temporarily rejuvenating himself using elixirs distilled from enzymes and proteins drawn from dead Astartes, and quite possibly including those who never even suffered the flaw either.

The legion as a whole had a obsession with perfection as a general concept but Fabius's first forays into bodily experimentation came when the legion assaulted Laeran, a world of reptilian creatures who were gene-engineered to perfectly carry out a specific task. Bewitched by the idea, Fabius eventually began to perform experiments on trying to improve the gene-seed, with Fulgrim's blessings.

During the opening movements of the Isstvaan Massacre (taking place before the actual murder-party itself) Fabius ended up saving the life of Nathaniel Garro, who would eventually go on to alert the Imperium to the Heresy. In retrospect that would probably make Fabius a dead man walking otherwise.

The Heresy

After turning full traitor, Fabius became the go-to guy for any kind of enhancement, to the extent that there were not many Emperor's Children in the legion who had not been under his knives in some form or other. He was part of the inner cabal of legion figureheads who attempted to exorcise Fulgrim and even found the time to fiddle around with mixing geneseed together (something unheard of at the time), eventually leading to a certain fellow called Honsou, and even toy around with both the original anathame and the (very incomplete) Primarch genome data. It was during this time that he first started on his hobby of turning men into horrifying inhuman monsters, something he refined considerably over the following millennia.

It was also during the Heresy that he received his surname from a daemon ascended Fulgrim, who accused him of being "full of bile". Somehow, Chaos Gods know why, the name stuck.

Post-Heresy

Because the Emperor's Children weren't involved in the actual siege of Emperor's Palace itself, they were in a strong position during the "Legion Wars" the raged in the Eye of Terror after the Heresy. While the Emperor's Children became wholehearted devotees of Slaanesh, Fabius didn't turn into a hedonistic sense addict, but rather rejected the Chaos Gods despite being aligned to Chaos. Despite their relative strength, the legion itself was divided between following Fulgrim, Eidolon, and Lucius. Fabius was one of the few authority figures left capable of keeping things together. After the Legion stronghold of Harmony was destroyed by the nascent Black Legion, many looked to Fabius to take command of what was left of the Emperor's Children. Fabius refused. Eventually, the rest of the Emperor's Children drove Fabius out of the Legion, but by that point his skill in cloning meant that he had plenty of opportunities to gain new subjects for experimentation while providing clones for the remaining Chaos Space Marines to make recruits from.

Present Day

It's hinted that he may have had something to do with the Obliterator virus (aka the turn-your-body-into-a-living-cannon virus) and there are rumors that he had a hand in screwing up the 21st Founding. He isn't a fan of Chaos, mainly for its role in destroying what little cohesion the Emperor's Children had post-heresy. He also sees its corrupting influence as running counter to his great work. He's also critical of the Emperor (beyond the usual traitor reasons) for stifling the growth of humanity as a psychic race. Despite having only very little time to live during the Heresy, he's survived through the millennia by cloning and jumping bodies on a regular basis, although the flaw in his geneseed will keep on being replicated and get progressively worse. He estimates that he'll only live for another few centuries, which he'll spend finding a cure and finishing his great work. He also occupies an odd place in the very loose and volatile hierarchy of the traitor legions, being both incredibly unpopular (he is wanted dead by the Dark Council of the Word Bearers, Fulgrim himself, and portions of almost every other traitor legion) and highly in demand for his skills (his knowledge of geneseed has saved more than one traitor legion from going extinct).

Most of his time is spent on the world of Urum, where he set up a loose organisation called the Consortium, a research facility / playground / artist's commune for other Chaos Apothecaries to practice their art in relative peace (and also partly addressing why there aren't many apothecaries in the traitor legions any more.

A major part of his "great work" is to create and perfect a new human race - the imaginatively named "New Men" - who would be superior to the Astartes and reclaim the galaxy from both chaos and xenos. The closest attempt he's made thus far are known as Glandhounds - men AND women (he's oddly egalitarian for a mad scientist, complaining that the Emperor was foolish to only let geneseed work on men) who are far stronger and more intelligent than regular humans, have very strong pack instincts and use them to bring down much larger prey. Like Traitor Astartes Fabius doesn't like. Unlike other examples of master-race creators in fiction, he seems entirely unconcerned about being the ruler of the new race or even being around when it comes about. It doesn't sound like a bad idea in itself but it goes without saying that old humanity would not be permitted to coexist with his new race.

As with a lot of big characters from earlier editions, his portrayal in the fluff is pretty inconsistent, varying between cackling mad scientist, sadistic torturer for the giggles, stern extremist, goal-obsessed manipulator, and weirdly paternal visionary. One audio adaptation gives him a thetting lisp, which is bafflingly amusing when imagining a space marine, let alone one using sexual torture devices on a primarch. Then again, he is jumping bodies a lot..

Send in the Clones

Bile has a hard-on for cloning technology, and has a track record for making copies of himself and others.

His first attempt was actually to clone Ferrus Manus since Fulgrim was feeling a bit guilty and wanted a do-over on turning his brother to chaos, though Fulgrim would keep murdering the clones because they wouldn't take the hint and change sides.

He later stole Horus's corpse and cloned it repeatedly, an act that pushed Abaddon out of his emo loser phase into becoming the scourge of the Imperium. Really though, Abaddon was just annoyed that Fabius has like four arms.

He's currently attempting to create a Clone of the EMPRAH. Using Sanguinius' blood. Let it never be said that Chaos is nothing if not ambitious. The Blood Angels managed to kill him and get the blood back, but he had already begun developing the clone at that point. (And as it turns out, they didn't kill him due to the clone bodies he has secreted throughout the galaxy.)

Crunch

On one hand, Bile has good stats and wargear: Feel No Pain through his Chirurgeon, Strength 5, a weapon that causes instant death (Rod of Torment), five attacks, and a particularly nasty poisoned weapon in the Xyclos Needler. On the other hand, his Rod of Torment does not ignore armor saves (unlike, say, the MURDER SWORD), his Xyclos Needler has really bad AP and sub-par range, and perhaps most damning of all, no Invulnerable save, unlike literally every other Chaos Character in the codex. So... Sucks, Right? Not quite. The reason Fabius Bile is taken, ironically, isn't for Bile himself; it's for his Enhanced Warriors trait, which gives a unit of Chaos Space Marines +1 Strength and Fearless. An enhanced Khornate CSM unit (Mark + Icon) rolls out 4 S6 attacks per Marine on the charge while being scoring and Fearless. While he isn't stellar in a normal CSM army (he's not a fighter nor does he enhance more than one unit of CSM), he really shines as an allied HQ — if you want a reasonably cheap CC threat for your pansy blueberries, take him and a 10-strong unit of Khornate CSM with meltaguns that can threaten massed infantry with the number of attacks, massed tanks with meltaguns/carnage combo and monstrous creatures with that Instant Death stick. Know that a Disordered Charge (aka multi-charge) denies you your Rage, so plan accordingly. Note that he can enhance one CSM unit in your entire ARMY, so take him in an Auxiliary Detachment for your Traitor Legion, and buff one of their Legion CSM units. 20 Infiltratring S5 Fearless Alpha Legion CSM anyone?