Main Source was a Canadian and American East Coast hip hop group based in New York City/Toronto, composed of Toronto-born DJs and producers, K-Cut and Sir Scratch, Queens DJ J.O.D and Queens MC and producer Large Professor. Later, another Queens MC, Mikey D, replaced Large Professor.

William Paul Mitchell, better known by the stage name of Large Professor, is an American rapper and music producer. Based in New York City, he is known as a founding member of the underground hip hop group Main Source and as a mentor and frequent collaborator of Nas. About.com ranked Large Professor at No. 13 on its Top 25 Hip-Hop Producers list.