A long time ago, the Wookiees of Kashyyyk realized a great evil would come into the galaxy. This was before knowledge of the Force had given way to the competing clans of the Jedi and Sith.
They remained out of the conflict for as long as they could. Eventually, the Clone Wars came to Kashyyyk, and the Wookiees had to make their stand. Unfortunately, it was too little too late. The Emperor had already executed Order 66, designed to assassinate every Jedi in existence, a fortuitous move considering he was a Sith and therefore seemed to have won the long, bitter feud at last.
Except he had miscalculated. The Jedi master Yoda survived thanks to the protection of the Wookiees. Except once more they were deadlocked in their deliberations on how to proceed. Only Chewbacca, Yoda's chief liaison among the Wookiees, chose to continue the fight. To do so, he had to leave all he had ever known behind, all his people, his world, his family.
For years, not knowing what had become of Yoda, he wandered from planet to planet, accepting increasingly dubious jobs in order to continue his search. One day he realized the freighter captain he had been working alongside was not the gruff rogue he appeared to be, but rather an idealist who was very much like the Wookiees he missed so much, directionless only because he lacked a purpose, an excuse to do the right thing.
One day Chewbacca found his opening. He was startled to discover a Jedi living on Tatooine, looking for a transport into space. He took it as an opportunity to manipulate his new friend into action, because he knew that the Jedi intended to aid the Rebellion against the Empire, the last best hope to end the great evil of the Sith.
Chewbacca only hoped his people were still safe. As part of his exile he had cut himself off from all contact with home. He wondered if anyone else had chosen to act, or if indeed all of Kashyyyk. He feared it wasn't so. But he now had a new hope.