Apoc was a crew member on the Zion hovercraft Nebuchadnezzar.
Apoc served in various roles, from running the tracing equipment for ejecting new Redpills from the Matrix, to being the main driver for the group. He wrote the Four Horsemen virus. He was frequently partnered with Switch.
He was alluded to the dark angel who brings the end. This was exactly what he did when he gave Neo his first handgun during the Hotel Ambush, marking the start of the end of Neo's 'innocence' as he first took up weapons with the intention to use them against others. Apoc was ruthlessly killed while still in the Matrix when Cypher, in an act of betrayal and in attempting to return his own body to the power plant, forcefully pulled out the Real World data probe actively connected to Apoc's headjack.