J Mascis (the J stands for Joseph) was the key member of seminal
rock combo Dinosaur Jr
from 1983 - 1997 (known only as Dinosaur
until 1986, when the name had to change for legal reasons). Lou Barlow
was also a Dinosaur member until he was unceremoniously (and sneakily) kicked out by J in 1989 after the release of the "You're Living All Over Me
J released a solo album "More Light" under the name J Mascis and the Fog in 2000, assisted by other rock luminaries Kevin Shields of My Bloody Valentine and Bob Pollard of Guided by Voices. This was the first "proper" album he released to not be in the Dinosaur Jr name, despite the fact that most of the instrumentation on the last handful of DJ albums was done by J alone.
J is known for being a difficult interviewee, a keen golfer (check out the video for "Feel The Pain") and a true master of the distorted electric guitar, producing enormous sounds of guitar noise and feedback of a quality up there with Neil Young. And those guitar solos... whoah.