J Mascis is an American musician, probably best-known as the singer, guitarist and songwriter for Dinosaur Jr..

Born on December 10, 1965 in Amherst, Massachusetts, Mascis founded the short-lived Deep Wound with his high school colleagues Lou Barlow and Scott Helland in the early 1980s. He then went on to found Dinosaur Jr. (also with Lou Barlow) in 1984, which achieved national success. After Mascis kicked Lou Barlow out of Dinosaur Jr. in 1989, he recorded several more Dinosaur Jr. albums, then went on to produce several albums with his new band, J Mascis and the Fog .