Another theory is that he is being cast through time in a similar manner to the [[Legion of the Damned]] appearing wherever and whenever he is needed. This is is subtly hinted at several times in the fluff, first with the minor inconsistency of his [[C'Tan|phase knife]] which exists outside of the [[derp|space-time continuum]], so Cypher has it in some instances, but does not have it in other encounters. Secondly, he can fuck with the established timelines and somehow confuse [[Tzeentch|Lords of Change]] whose JOB it is to know the future ''(see above)'' and thirdly, Cypher ''(and/or [[Zahariel]])'' is somehow connected to the '''Ouroboros''' which was concealed on [[Caliban]], which if you know your philosophy is the representation of time recycling itself eternally. So he could be time travelling, or waiting for eternity to swing back around to try things a little bit better each time round.
The most common and likely theory is that Cypher was the last Knight of the Order of Lupus, a Knight Order that was actually a Chaos Cult that was wiped out by Lion El'Jonson but he was allowed to join the Order and later the Dark Angels and became The Lord Cypher, a rank of the Dark Angels. He is the person who convinced Luthor to turn against The Lion. It is fairly clear that that was the case during the Horus Hersey, but if Zahariel is not the current Cypher, then it is likely still the Knight of Lupus
(with his destiny traded with Epimetheus ).
==What he's up to==