Expanded Universe has stated that Han, while in the Imperial Academy, freed Chewie from the Empires enslavement, because all the wookies were apparently enslaved by The Empire at some point. Cheiw has a life debt for sorting him out.
dont believe the expnaded universe its not GL its other people that have followed on the story in GL's eyes starwars is the movies not the books unless its the starwars book of the film.
It actually makes perfect sense, that Han rescued Chewie from enslavement. What could better warrant a life-debt?
It was made even larger a deal when in the Chewbacca comic-book anthology, it was explained that Han was actually the cause of Chewie's enslavement.
Well, this is somewhat idiotic, because Chewie being a slave and Han Solo rescueing him from slavery has been every bit "canon", (and as close to being "canon" as anything can get), as was also the fact that Vader was sent into a volcano by Ben, (as said by GL back in the 70's-80's).
In fact, Chewbacca being a slave and Han rescueing him has been apart of the "EU" since the very beginning. It was talked about and insinuated in Brian Daley's Han Solo Trilogy back in the 70's, and he have talked to GL long and hard to understand the characters to their full extent.
However, GL almost ruined this by putting Han Solo in the early drafts of RotS, being raised by Chewbacca on Kashyyyk.
when you say dont beleive the EU, what makes you think that this doesnt get the thumbs up from GL? he takes care of the universe, and makes sure that all stories are sound before letting them get published. i'm sure if he could live for a another century he'd make more films, before and after. realistically of course that wont happen. its also hard to get actors to return to the same roles. if something in the EU was wrong, it wouldnt have gotton published in the first place. of course theres conflicts, but when isn't there?