George McFly was the father of Marty, as well as Marty's brother Dave and sister Linda. He met and fell in love with Lorraine Baines after she took care of him when her father accidentally hit him with the family car. As a teenager, George was a "nerd" who never stood up for himself, allowing bullies like Biff Tannen and his gang to pick on him. Biff would often force George to do his schoolwork for him, and this continued on into adulthood in 1985, where George continued to allow Biff to pick on him and extort favors from him. George's destiny changed when his youngest son Marty accidentally travelled back in time to 1955 and interferred with Lorraine and George's first meeting, almost bringing about his own non-existence.
In order to save himself and his siblings from fading out of existence, Marty was forced to befriend his teenaged father and George was taught by his future son on how to properly stand up to Biff and his gang. He saved Lorraine from being raped by Biff, and was never picked on by the bullies ever again. When Marty returned to 1985 he discovered that due to the altered timeline, his father was now a successful science fiction author. His marriage to Lorraine remained happy, although by 2015 he was experiecing severe back problems and was forced to get around using an anti-gravity suspension device.
When the old Biff from 2015 went back in time and gave his teenaged self Gray's Sports Almanac, and Biff thus became the richest and most powerful man in Hill Valley, history changed a third time when, sometime after Marty was born, Biff murdered George by shooting him. He was buried in Oak Park Cemetery, and Biff married Lorraine. Luckily, this horrible tragedy was averted when Marty went back to 1955 again and stole the almanac from the young Biff, erasing the Biffhoriffic 1985 from existence, meaning that George was once more alive, married to Lorraine, and a successful author.