Marcus Gates is a character portrayed by Lee Tergesen on Castle in the episode 3XK. Gates was acting as the serial killer known as 3XK, later discover to be Jerry Tyson, who gave Gates all the info he needed to pretend to be him, thus allowing Tyson to be released from prison early as part of a deal to provide the investigating team with evidence that Tyson also provided Gates with money to pay for vital surgery required by Gates's foster brother. Castle and Beckett were eventually able to discover this scheme of theirs and he was sent back into custody.