TSK · Numbers 32:40

and the rest of Gilead, and all Bashan, the kingdom of Og, gave I to the half-tribe of Manasseh; all the region of Argob, even all Bashan. (The same is called the land of Rephaim.

This was the lot for the tribe of Manasseh, for he was the firstborn of Joseph. As for Machir the firstborn of Manasseh, the father of Gilead, because he was a man of war, therefore he had Gilead and Bashan.