Matthew Joseph Thaddeus Stepanek (July 17, 1990 – June 22, 2004), known as Mattie J.T. Stepanek, was an American poet (or as he wanted to be remembered as "a poet, a peacemaker, and a philosopher who played") who published seven best-selling books of poetry and peace essays. Before his death (at the age of 13) he had become known as a peace advocate and motivational speaker.

Mattie Stepanek, who was suffering from a hereditary muscle disease and knew that he would die young, had an exceptional vision of life. As a child he held talks about peace with, among others, former President Jimmy Carter, his great example.