M'Baku is the leader of the Jabari Tribe in Wakanda. He was an arrogant rival turned ally of T'Challa after he yeilded in ritual combat. He's got a funny sense of humor and after leading his tribe into helping T'Challa defeat Erik Killmonger, W'Kabi, and the Border Tribe, he for the first time earned a seat in the Council and with the Jabari know designated as Wakanda's national guard, all the five tribes stand united for the first time.
He and the Jabari rallied with T'Challa and the Avengers at the border to defeat the Black Order and the rest of Thanos' forces. After Thanos snapped his fingers with all 6 infinity stones in hand, M'Baku survived only to watch his people and most Wakandan soldiers get taken out of existance.