As the leader of the Jabari, a.k.a. the Mountain Tribe, M’Baku believed that it was a mistake for Wakanda to turn its back on tradition and lean too heavily on technological advancement, hence why he fought T’Challa for the throne.
By the end of the movie, though, he helped T’Challa defeat Killmonger and his forces, so they seem to be on good terms now.
M’Baku has been one of T’Challa’s chief adversaries in the comics for decades, but sticking him in a white gorilla suit and calling him Man-Ape almost certainly would have been problematic for the MCU.
But along with ditching his super villain gimmick (though his costume does have some white gorilla fur on it), Winston Duke’s M’Baku was reimagined as more of a rival to T’Challa in Black Panther rather than a nemesis.