It's a safe bet that if you're younger than 25, you probably have no idea who Leon Russell is, but there's still a chance you've heard him play. For years the Tulsa, Okla., native established his career as the ultimate session musician, working in the studio and tour with artists as varied as Jerry Lee Lewis, Marvin Gaye, John Lennon and Frank Sinatra. An arranger, producer, pianist, guitarist, record company owner, and bandleader, Russell is of course a respected songwriter in his own right, finding success with his set of blues-tinged country tunes such as “Tight Rope,” “Lady Blue,” and “A Song for You,” a ballad which remains one of the most regularly covered tunes. Accompanied by his signature snowy white beard, Russell is scheduled to perform at the Hat Factory on Friday, Jan. 8, at 9 p.m. $20-$30. 788-4281.