The Assassin protagonist of Assassin's Creed III is commonly called Connor.
Connor's Kanien'kehá:ka birth name is Ratonhnhaké:ton, while Connor is the name he uses in much of the game. He is the son of Haytham Kenway and grows up in a Kanien'kehá:ka community. After his village is threatened, he seeks guidance from Achilles Davenport and joins the Assassin cause.
His story unfolds during the American Revolution, with major locations including Boston, New York, and the American frontier. Connor becomes involved with figures such as George Washington and Benjamin Franklin, while the game dramatizes the conflict between the Assassin and Templar factions.
The answer is conventionally given as Connor because that is the protagonist's widely used English name in the game and its marketing. Ratonhnhaké:ton is not a different character; it is his birth name. Haytham Kenway, his father, is also playable in the opening sequence but is a Templar rather than the principal Assassin protagonist.