Brother Caiphas Cain
The Changer of Ways dislikes constants. The sameness was something the Architect of Fate could not abide.
He wished change upon creation in the vastness of space and time and infinity of possibilities and change they did.
Primarchs could become female, their personalities shifted by different experience, they could be relocated or have their fates altered.
Greatest of the Aeldari, those players of Game of Destiny, even their gods were subject of his whims. Isha had fled the Youngest in multiple strands of time. Vect was shanked, poisoned, devoured and even served to a particularly depraved Aeldari lord as dessert while still in his mother's womb.
Even Tzeench himself was not beyond being winked out of existence.
Yet here was this sideburned, self-professed coward loyal servant of the Anathema, lucky, supremely misunderstood Caiphas Cain, who no matter what, when and how, somehow possessed the exact same traits, and was always saddled with the title of Hero of the Imperium.
And yes, being sarcastically referred to as such by a bunch of Inquisitors, in case of that Warmaster of Chaos variant, still counted.
This could not stand. This called for a more cunning and convoluted plan. The best kind of plans.
Why not make him know no fear and this time for real? Besides heroes with legendary feats among the Space Marines were dime a dozen and when the likes of Dante and Marneus Calgar were around who would look at a poor of Caiphas Cain as HERO OF THE IMPERIUM anyway? These were good enough changes from the usual fare and Tzeench was happy with them.
Just in case it was arraigned for a chapter with a mutation that made them hairless to pick Cain.
Such was Caiphas Cain's lot, to be picked by the crusading chapter Blazing Saddles, known for being hairless, taller than average Space Marines, avid Codex Buggerers and favouring full frontal assaults, on his way to Schola.
And while his body did indeed took to the Khan's geneseed and he was made into a tall, even by Space Marines standard, bald example of his kind, for some odd reason his mind never took to hypnoconditioning.
Normally that would've been a fatal flaw. But Caiphas Cain was nothing if not resourceful, strangely lucky and he showed no outward sign of not being what he was meant to be.
Every live target placed in front of him, be they pitiful xenos, youthful heretics or failed aspirants, were killed without hesitation or mercy. Keen survival instincts and self-preservation mistaken for zealous brutality.
Fight or flight instincts, sharped by very real fear of death, and knowledge that flight would mean death anyway, had the same result as fearlessness of a typical Astartes.
Common sense and desire to be out of harm's way, a strange sort of luck that sent Cain into thickest, most crucial parts of the battlefield and his nigh-peerless prowess with his trusty chainsword and bolt pistol that saw him throuh, was seen as the sort of glory-seeking cunning prized by the Chapter's leadership.
In the face of overwhelming success after overwhelming success the Lords of the Chapter were more than willing to overlook little things like the Captain's (youngest in their five thousand years history) near-Wolves of Fenris like alcohol consumption.
But Caiphas Cain's star would not stop rising just yet. After heroically, and for the fifth time slaying Lucius the Eternal (later returning in body of the Inquisitor who masterminded his latest death at hand of Cain, and swearing vengeance on Cain yet again) during the 13th Black Crusade, Cain valiantly joined the race to Ultramar and partook in events leading to return of Primarch Guilliman.
Cain then followed the Primarch to Terra and distinguished himself during the Avenging Son's stay there, showing a surpring grasp of courtly affairs for a Space Marine and unearthing and neutraliseing several plots against the stability of the Imperium.
His achievements overwhelming, and eye of Terra and the Imperium upon him, in Cain Guilliman saw yet another tool for boosting the near-broken Imperial morale.
And so, in the Triumph at the beginning of Indomitus Crusade, among other things Caiphas Cain was declared a Hero of the Imperium, and the very first Space Marine of Old to cross Rubicon Primaris.
Cain, unwilling but unable to deny the only person to see through him and say that to his face, agreed, crossed Rubicon Primaris successfully and in addition to growing even taller, became the very first Blazing Saddle battle-brother in known history to grow hair. He celebrated his new hairiness by growing a magnificent pair of sideburns.
Not long after Caiphas Cain killed Lucius the Eternal for the sixth and final time, using the dead champion's sword to detonate Daemon Primarch Fulgrim with help of the last smelly scion of a smelly line of Valhallans, in such a way that the nearby Pharos device fired Prince's essence at the Tyranid Hive Mind, and severely wounding the entity and greatly weakening the Hive Fleet as whole, a council of the returned Primarchs declared him THE HERO OF THE IMPERIUM.
Not long after anyone with a lick of psychic sense heard a mollusk-like cry, declaring it would no longer answer to "changer of ways" or "architect of fate". It was left unsaid how nobody knew what a mollusk cry sounds like.