- Doc: "Marty, get in! This timeline's been compromised!"
- Marty: "No kidding!"
- — Upon realizing the events in the past had been tampered.
1986F was a timeline created as a result of the actions of both Marty McFly and Emmett Brown in 1931. By removing Arthur McFly from the area, this allowed Irving "Kid" Tannen to become ever more powerful, eventually resulting in a crime family that was the fifth most dangerous in California. In this timeline, Biff Tannen had two brothers, Cliff Tannen and Riff Tannen. On behalf of Kid, they beat up citizens of Hill Valley when it came time to pay up, creating general terror and eventual abandonment of the city. It was later replaced with a corrupt, totalitarian society in another alternate 1986 that was made when Doc and Marty went back to 1931 to fix the timeline.
Although it is not specifically mentioned, it is likely that Danny Parker Jr. and, consequently, his daughter Jennifer Parker were never born in this timeline, as Officer Danny Parker's girlfriend Betty left him in 1931, before they were to have been married, after his failure to capture "Carl Sagan", which he blamed on "flying space cars". This is supported by the fact that George McFly has no idea who Jennifer is.