In Back to the Future Part II, Doc picks up Marty in 1985 and takes him to 2015. Then old Biff realizes the Delorean is a time machine. Old Biff steals the Delorean and travels from 2015 to 1955 to ...
Although Marty is only in 1955 for one week, he plays a pivotal role in getting his parents together. He even briefly dates his mother. So, considering he plays such a pivotal role, does it make sense ...
There are many movies and TV episodes in which a character "crosses his own timeline", sometimes even meeting his past or future self (e.g. The Day of the Doctor). Technically, I should say meeting ...