Robert Knepper has already been promoted to series regular status on NBC's Heroes, on which he will make his debut this fall.
Knepper was originally signed to play the mysterious Samuel for six episodes, and has so far appeared in every episode, says the Hollywood Reporter.
Samuel is "the reluctant ringleader of a carnival," Knepper shared at the San Diego Comic-Con last week (see video below, at the 14:00 mark). In the wake of his brother's passing, "he's made a decision that his life is not going to be the way it used to be," so he sets out to make some changes. Samuel "one-by-one lures the heroes into helping with that plan," Knepper said.
Knepper is best known to TV viewers from his run as Prison Break's sinister Theodore "T-Bag" Bagwell. Heroes kicks off its fourth season on Monday, Sept. 21, with a two-hour premiere.