Unknown (presumed dead)
V. King was a civilian technician assigned to Marine Headquarters in Mars City. He was responsible for monitoring communications to and from Marine Headquarters.
When the player meets V. King in Doom 3, he is seen responding to a request from Delta Labs for additional security. If you try to converse with him, he will (like most characters) tell you he's too busy to talk.
His fate is unknown, though he was most likely killed or turned into a zombie during the demon invasion.