He rips through the streets of a quarantined, zombie-infested Manhattan killing Marines, and anyone who stands in his way.
He has superhuman strength, speed, and hops. His arms turn into a variety of deadly blade-like weapons. He can consume people to replenish his health, see their memories, and take their physical appearance. He consumes people that know how to drive/fly military vehicles such as apc's, tanks, and helicopters, all of this which he can hijack at any given time and kick serious ass behind the driver's seat. He's also got a magical hoodie that somehow manages to stay on his head no matter from how high he falls, how much he rolls, how many missiles get shot at him. Did I mention he can pretty much fly?
Alex Mercer can be seen in the game Prototype, where he finds himself trying to figure out who made him into this mutant badass, after which he makes them pay.
Another civilian brutally slaughtered by the badass known as Alex Mercer.