Chewbacca the Wookie and Wookiee General Tarfful were responsible for Yoda's escape when Emperor Palpatine ordered the Clone troopers to turn on the Jedi during the infamous Clone Wars.

Han Solo spent about five years in the Imperial Starfleet. Han was ordered to destroy a slaving vessel full of Wookie slaves, but Han refused and instead he aided in the Wookies escape. Chewbacca, as he was called, endebted his life to Solo. Solo was stripped of his command and was dis-honorably discharged. (there's a bit of confusion there as to how the pair actually met....this is the way I always thought of it, but in the Han Solo trilogy they tell a different story...the main thing was the same, Han was ordered to kill Chewbacca, refused, and was discharged from the Imperial Navy)

The duo's early career was spent doing smuggling runs for various masters, including the Desilijac clan of the Hutts. Jabba the Hutt thought up a plan that would devastate the Besadii clan by eliminating their spice processing facilities on Ylesia. He contacted Han Solo's ex-love Bria Tharen to do the job. Tharen had become an undercover operative in the growing resistance movement opposed to Emperor Palpatine. Han and Bria fell in love all over again. Accompanied by Lando Calrissian, Solo agreed to join the assault on Ylesia for half the spice profit. Commander Tharen and the Rebel troops however double crossed their smuggling allies and took all the spice for themselves. Han was doubly crossed. His love betrayed him, and his comrades thought that he was in on the whole deal. Calrissian swore he never wanted to see Solo again. Betrayed and rejected Han and Chewbacca went back to Jabba to make a Kessel Run. When they were pursued by Imperial customs vessels Solo was forced to dump his load of spice. This angered Jabba greatly. He needed to raise money to pay Jabba, so he went to Tatooine were he would meet up with and old familiar face Boba Fett, not to kill him, but to make a promise he had kept, to tell Solo of Tharens death so that he could inform her family. He also met up with two local desert dwellers offering to pay him for transport to Alderaan (Luke Skywalker and Obi-Wan Kenobi and two droids). And once again, there was a bounty placed on his head.