John Proudstar was part of the all-new, all-different X-Men roster in 1975. He was brought onto the team alongside Wolverine, Storm, Colossus, Nightcrawler, Sunfire, and Banshee. Thunderbird accompanied them (minus Sunfire, who immediately left the team) on a mission to stop Count Nefaria and his Ani-Men. This mission ended with Thunderbird dying on Nefaria’s exploding escape jet.
Thunderbird was a mutant who possessed superhuman strength and endurance, as well as extremely high coordination, senses and reflexes. His muscle tissue was three times as dense as that of a normal human being’s and was distributed in such a way as to give Thunderbird massive shoulders, arms, and thighs.