Kreed was a Celestial Guardian. At some point he abandoned his duties and fell, choosing instead to pursue the power of a corrupter, corrupting and feeding upon souls - especially metahuman ones.
He attempted to obtain the Threads of Fate but was thwarted by Weaver who fled with them.Over time his appearance changed from that of a handsome man to a terrifying demonic visage.
It is unclear what his purpose for these corrupted humans was. Following their corruption they all went on uncontrolled, seemingly pointless rampages.
Kreed was ultimately defeated and killed by the combined efforts of Weaver and SHELL while trying to capture the soul of Claire Despoir.
Kreed was able to pull metahuman souls from their bodies, corrupting them and turning them into his "harvesters". He absorbs these energies to feed which also puts the metahuman into his thrall. Corrupting a metahuman can also increase their power.
Kreed was also capable of tearing ordinary human souls from their body and feeding on them but he considered them beneath his notice.