In Assassin's Creed Rogue, the Assassin who joins the Templars is Shay Cormac.
Shay Patrick Cormac begins the game as an Assassin operating in the North Atlantic during the eighteenth century. After becoming disillusioned with the Brotherhood's methods and surviving a disastrous mission, he defects and joins the Templar Order. Rogue tells the series' conflict from a Templar-aligned perspective, making Shay's change of allegiance its defining premise.
The game is set during the Seven Years' War and connects its story to Assassin's Creed IV: Black Flag and Assassin's Creed III. Shay encounters characters from both games, including members of the Kenway family and Assassin leaders in colonial North America.
Cormac is Shay's surname, not his first name. Kenway belongs to Edward, Haytham, and Ratonhnhaké:ton's family line, while Dorian and Frye are surnames associated with later protagonists in the series.