The leader of the Dread Doctors whom speaks the most. In 5x01 - Creatures of the Night, the Surgeon refuses to give Belasko another chance after he fails to kill Scott, that their time is limited. He kills Belasko with a rapier sword held in his cane.
In 5x02 - Parasomnia, the Dread Doctors have summoned Tracy Stewart to their lair. He taunts her that sheisn't asleep, she's "awakening". He injects her with an overlarge needle, which Tracy roaring with the gold eyes and claws of a werewolf.