He was in the 3rd edition Codex* and could also be taken as a choice for Imperial Guard.
His rules aren't very good
IMHO however.
I've included him in my
Chaos Space Marine Fandex for what it's worth so you may find the rules there better than his previous ones, which I'll look up now for you...
*
Automatically Appended Next Post: He had Master-crafted pistols, a power weapon, the same stats as a current Chaos Lord with the
WS &
BS swapped around as well as initiative 8!
He's an elites choice for Chaos or Imperial Guard, costs the same as 10 Chaos Space Marines and is an independent character.
If he joins a squad you roll a
D6 each turn and on a 1 all members do not do anything for the rest of the turn. This doesn't effect Cypher himself or Fallen Angels which are effectively Chosen
CSM's with
ATSKNF.
He has a 4++ on
3D6 against any attack that reduces him to 0 wounds, if this save is passed then he is removed from the game but doesn't count towards victory points.
He can fire both pistols and/or fire them twice if he remains stationary.
Deathwing or Ravenwing must charge him if they can.
*I can't imagine it's a problem posting rules as A) he no longer exists and B) I've been deliberately vague.