Tom originally worked for the NYPD before being caught up in a battle between the New Mutants and the Demon Bear. He and Sharon Friedlander were magically transformed from being physically caucasian to Native American. Unable to explain their new bodies, Tom and Sharon resided at the Xavier Institute and joined the school staff.
After the Mansion was destroyed during "Inferno", Tom and Sharon relocated to Muir Island. They participated in the defense of the Research Center from an assault by the Reavers.
Much later, Tom and Sharon went undercover at a private school to supervise a latent mutant. When the Acolytes attacked the school in search of the youth, Tom used a shotgun to kill Eric Kleinstock. Tom held the Acolyte attack off long enough for the X-Men to arrive, though Sharon perished.
Tom joined the staff of the Massachusetts Academy when the school opened to human students. He acted as gym teacher, and began more intensive training of Generation X. When the school closed, Corsi transferred back to the Xavier Institute. He continues to teach physical education at the Institute.
After M-Day, Corsi was let go and his current whereabouts are unknown.
Tom is a human, transformed by the Demon Bear to resemble a Cheyenne. Tom has increased strength due to his transformation by the Demon Bear, though it is not classified as super strength. Tom also possesses increased speed and reflexes.