Mattie Silver is the name of a character in the book Ethan Frome by Edith Wharton. She is Ethan's wife's cousin and he has feelings for her. [He's a bad person in my opinion and so is Mattie of course, in my opinion]
A famous bearer is Mattie Stepanek, a boy with muscular-dystrophy who amazingly lived to be 12 years old! He was extremely intelligent and started writing poetry at age 3. He was a peacemaker.