If George Lucas had listened to Mark Hamill's creative direction when making the original Star Wars trilogy, well, we would have had a very different franchise.
Hamill revealed on Twitter that before he knew Carrie Fisher's Princess Leia was his sister, he wanted Boba Fett to be his mother. He apparently thought having Boba Fett be Luke's mother or a double-agent for the Rebels was one way to top The Empire Strikes Back's revelation that Darth Vader was the character's father.
Then there was the time I pitched Boba Fett as Luke's mother. I have always been more than willing to generously share my many, many terrible ideas in the off-chance we might stumble across one that could actually be useful. At the time, I didn't even know Leia was my sister. https://t.co/nurhFZZS01— Mark Hamill (@HamillHimself) November 16, 2018
That change would have certainly made the early films even more of a space soap opera. However, Lucas didn't take to Hamill's vision, and we ended up getting Boba Fett as a bounty hunter working to further Vader's galactic war.
The change would have certainly affected the prequel films in a major way, with Boba's father Jango serving as the genetic template for the clone troopers. It would have also changed several major plot points surrounding Natalie Portman's Padme Amidala, whose mortality was integral to Anakin Skywalker's turn to the Dark Side.
Hamill will reprise his role as Luke Skywalker in J.J. Abrams' Star Wars: Episode IX, which stars Daisy Ridley, Adam Driver, John Boyega, Oscar Isaac, Lupita Nyong’o, Domhnall Gleeson, Kelly Marie Tran, Joonas Suotamo, Billie Lourd, Keri Russell, Matt Smith, Anthony Daniels, Billy Dee Williams and Carrie Fisher, with Naomi Ackie and Richard E. Grant. The film is scheduled to open on Dec. 20, 2019.