Steve Willits

Steve Willits was a scientist working for the UAC on Mars. His wife is Dr. Jenna Willits. He was mutated into an imp that killed Goat, and as a result was killed by Reaper. His body was later dissected by Samantha, through which she discovered that the monsters are human.

The character's name is most likely a nod to Tim Willits, id Software's creative director.