Unknown (presumed dead)
K. Tang was a maintenance worker assigned to Mars City, and has been working there for four years.
When the player meets K. Tang in Doom 3, he is watching the news, but will greet you and offer some advice about your stay on Mars. He will sternly advise you to not wander into places you're not supposed to.
His fate is unknown, though he was most likely killed or turned into a zombie during the demon invasion.