Joey Baines.

“Better get used to these bars, kid.” —Marty McFly

“Jailbird” Joey Baines (born 1954) was the fourth child of Sam and Stella Baines. He would grow up to spend many years in prison for an unknown offense. On October 25, 1985 he failed to earn his release on parole for at least the second time. When Marty McFly traveled back to November 5, 1955, he met his uncle Joey at age 1 behind the bars of a crib wearing a black and white striped shirt. Stella noted that he enjoyed being in his crib, as every time they took him out he would cry. In the 1985a timeline, Joey was still noted as being in jail. In 2015, Joey was still in jail. (In a deleted scene from Part II, Marty of 2015 says “Mom, let’s wait and see if Uncle Joey makes parole.”) Joey appears to have a psychological mental imprisonment complex. It’s likely that him never making parole is an intentional effort on his part in order to remain behind bars. An early script of Back to the Future Part II showed that Joey, in his early teens in 1967, enjoyed locking himself in his room and eating nothing but bread and water.

—http://backtothefuture.wikia.com/wiki/Joey_Baines