“No, I am your father.” Five words that changed not just the life of Star Wars’ Luke Skywalker but movies in general. On May 21, 1980, the highly anticipated sequel to the 1977 mega-hit Star Wars hit theaters. It was called The Empire Strikes Back and boy did it ever live up to that title. After losing the Death Star, the Empire forced the Rebel Alliance off its base on Hoth, captured one of its leaders in Han Solo, and severed the hand of the man most responsible for the destruction of the Death Star, Luke Skywalker. Oh, Luke also found out his mentor Obi-Wan Kenobi lied to him and that his father wasn’t murdered by Darth Vader...he was Darth Vader. You probably know all this already. And if not, well, 40 years feels like an adequate spoiler warning. The thing is, when we say “spoiler warning” you know what we mean now. It’s a phrase that announces there’s a secret or reveal in a plot that’s best experienced during a story, not before it or out of context. Back in 1980, though, that sentiment was still relatively alien. In fact, if you look back at history, protecting the massive surprise at the end of The Empire Strikes Back was one of the things that began to change all that. In the above video hosted by our editor Jill Pantozzi, io9 explores the origins of the Star Wars bombshell and follows its impact across four decades of film history. Check it out. For more, make sure you’re following us on our Instagram @io9dotcom.