Haytham Kenway is the Templar leader revealed in Assassin's Creed Rogue.
Haytham is the Grand Master of the Colonial Templars during the period covered by the game. He is also the father of Connor, the protagonist of Assassin's Creed III, and the son of Edward Kenway from Assassin's Creed IV: Black Flag, linking three generations of the Kenway family.
Rogue is played primarily through Shay Patrick Cormac, an Assassin who becomes disillusioned with the Brotherhood after a disastrous mission. Shay defects to the Templars, and Haytham becomes his superior within the organization. This viewpoint reverses the usual series structure by making a former Assassin hunt his old allies.
Charles Lee is another important Templar character, while Achilles Davenport is Shay's former Assassin mentor. Neither is the Templar Grand Master identified by this question. Rogue was released in 2014.