Ebonite

Mister  was an alien technology trader. He was a gestalt being.

Biography
He had an agreement with Cleo Hunsicker requiring her to deliver him all alien artefacts that the Cult of the Black Pyramid did not require. When he detected a time anomaly in the journal left to Cindy Wu by Gabby Gonzalez, he demanded the journal to be handed to him. Only the interference of Jack Harkness saved the day. Jack shot Mr Ebonite causing him to break into many little copies of himself. (COMIC: Cindy, Cleo and the Magic Sketchbook)

He abducted Jack Harkness, Cindy Wu and Cleo. The Monaxi, his servants, activated a time bridge and brought the Tenth Doctor and his crew to the Arena of Fear as well. After Ebonite stated that "anybody could be their enemies", Tony, Gabby and Unta were under his control inside the Arena of Fear.

He was defeated by Gabby, who had released herself from his control. Afterwards, he split into many small versions of himself, which ran away, some of them being killed. (COMIC: Arena of Fear)