Iron Will was a First Era minotaur, specializing in extremely aggressive and enthusiastic motivational speeches. He made a small fortune on his personal pony coaching, before marketing his "Iron Will's Muscle Oats" brand of athletic supplements.
His company, Iron Will's Pony Performance Products, was a sponsor of Rainbow Dash.
His genetic material, stored at Amity, is the only known sample of minotaur DNA. Thus, even at the end of the novel, their species seems doomed. No known females exist.