Han Solo

When Coppola and Lucas (close friends and filmmaking buddies) were planning Apocalypse Now (which George Lucas was originally supposed to direct) they gave a small role to their carpenter, Harrison Ford, in return for Ford's work on a desk for Coppola's office. Ford also got a role in Lucas' American Graffiti a few years prior this same way. During the casting for Star Wars, Lucas needed someone to read Han Solo's lines while the actor's auditioned for Luke. He quickly asked Ford to do it, and afterwards, one of the producers there came up to Lucas and pointed out that he already had his Han Solo in Ford. (Thus beating out Kurt Russell for the role).