Agent Smith is the main villain from The Matrix. In the first movie, he's no different from any of the other of the machines' agents, capable of taking over the bodies of people connected to the Matrix and with the purpose of killing anyone in the Real World who tries to hack into it. He kills exactly 0 people in the first movie, but is killed by Neo, then was alive again in the next two, and somehow could now take over anyone, take over multiple people at once, and... Meh, just watch the damn movies, if you dare.
He's made cameo appearances in a few of Thorvald's GMod comics, and a character with his model appeared in the first comic CivGeneral made in DYOS 11, although his role appears to have been dropped. Major Kusanagi expressed distrust in him.