Haytham Kenway is a Templar who came to the American colonies in 1754. From what we've learned, Kenway was sent here by Grand Master Reginald Birch, with a dual mission: establish his own Templar group to rival the colonial Assassins - and searching for clues about artifacts related to the First Civilization. And when a Grand Master tells you to do something, you do it. Even if it's just a Chess Grand Master.
Kenway didn't find the artifacts he was looking for. He did, however, recruit a small, dedicated band of Templars. He also attempted to forge a relationship with the Kanien'kehá:ka in the frontier, and one woman in particular, Kaniehtí:io. The two were briefly lovers - and however brief it was, it was enough, because Kaniehtí:io, unbeknownst to Haytham, ended up raising their son, Connor.
I'm guessing it was Kenway who became Grand Master in the colonies, and therefore the man responsible for the 1763 attack on the Colonial Assassins. That attack wiped out most of the membership and almost all of our records from that era. It's never been clear exactly what happened in that attack, or how Kenway managed to make it such a complete surprise.
In any case, I don't like this guy. Sorry to use such strong words.