Mortimer Martin "Mert" Hackett (November 11, 1859 – February 22, 1938), was an American professional baseball catcher. He played in Major League Baseball from 1883 to 1887 for the Boston Beaneaters, Kansas City Cowboys, and Indianapolis Hoosiers. His older brother, Walter Hackett, and cousins Walter Clarkson, Dad Clarkson and Baseball Hall of Famers John Clarkson, Tim Keefe and Joe Kelley (all born in Cambridge, Massachusetts) also played in the majors.