I thought he was cables biological son. Although Marvel may have gone back and forth on the answer, changing thier minds. I thought Tyler was Cables son, and then kind of fell in with Stryfe or got tricked into thinking Stryfe was Nate, and eventually through Stockholm Syndrome began to hate his father. Like I said, maybe I am wrong, maybe Marvel has gone back and forth on the issue, but thats what have thought since the 90s.
Pretty sure that's the official word on paper, but I think hints were dropped that maybe not.
This goes into the story more: