Called "The Enticer" by those who know of - and fear - him, Regulus was a battle-brother of the Emperor's Children before their fall into Chaos, and fought at the Battle of Terra during the Heresy.
Regulus has a silver tongue, and over the centuries it is said he has led countless Chaos cults on a hundred different worlds - and there is nothing he loves more than the adoration and worship of followers.
Ultimately, Regulus' cults - almost all Slaneesh devoted, though some have been devoted to Chaos Undivided - have grown so debased that they can't help but be discovered. And he has always walked away to start up some other cult on some other world as his former followers were slaughtered in his wake.
His most recent cult was based in the Calixis sector 50 years ago, a group he called the "Adherents of Pain and Pleasure." They were rooted out by the Inquisitorial presence of the region, and Regulus was very nearly killed in the ensuing raid - but fled into the Screaming Vortex to recuperate and plan.
Patience is among Regulus' few remaining virtues. He knows that the greatest delights can come from anticipation - a trait that has kept him from becoming one of the jaded husks so many of his former brothers have. There are still many new and terrible sensations that he has yet to explore, and many dark impulses he has purposefully repressed... for now. The price of his centuries-long restraint is that he has also not been as blessed as so many of his former battle-brothers have, favoured as they are by the Prince of Pleasures.
Regulus has had his successes, and his failures, during the Long War, and has accrued a bit of a reputation. It may be that he's just one big opportunity away from the greatness he so deeply desires.
Rita was one of hundreds of street urchins born outside of the light of the Emperor. She lived for as long as she could remember among the ruins of Sacrgrave, scraping by a bare living on the dregs of the pirate civilization, addicted to stimms and lho sticks since she was old enough to hold them. Likely, she was meant for an early death or a cruel future as a slave to the pirates of her world. But fate works in strange ways in the Screaming Vortex.
Whatever whim it was that led Regulus the Enticing to walk through the lower levels of the shattered city early one evening, it led him to come face-to-face with the girl. Rita had heard tales of Astartes... but like so much else she assumed they were myths, legends to scare the little kids. When she beheld Regulus in all his terrible glory, it was a profound experience. Life changing.
Regulus didn't say a word to her, but she followed him. She has never stopped.
Rita is a 13-year-old girl, and from a very poor background, which is why her stats are fairly low for an "average human." She is slight, dirty, and largely unremarkable. But, as Regulus has learned over the years, she has her uses. She's sneaky, deceptive, and can lay on the "street urchin charm." She's also got a talent for voices, and a sharp ear. Rita can get places and move around in a way that her master simply can't. She also practically worships the Enticer, seeing him as a godlike saviour who took her away from a pathetic life, and shown her the glory and horrors of the cosmos. Her orthoproxy talent represents that unwavering loyalty far above and beyond what her Willpower score should allow.