A long time ago, the Jedi named Yoda met a Wookiee named Chewbacca. Yoda had been flush with the belief that the Jedi had finally done away with the threat of the Sith. After the death of Darth Plagueis and disappearance of his apprentice, there seemed to be none left of the practitioners of the Dark Side. Chewbacca, however, cautioned him that it wasn't over. Yoda didn't believe him.
Many years passed. When Yoda came back to Kashyyyk, it was because of the Clone Wars. It had recently been determined that the Sith were back. It was Chewbacca's contention that they had never gone in the first place, but he chose not to mention it. Instead he fought alongside Yoda in a fierce defense of his home world. When the Clone Troopers turned on Yoda, revealing their allegiance to the Sith, Chewbacca ensured that his friend survived, strained relationship or not.
Again they lost contact. It was Chewbacca's understanding that the Jedi went into exile. For years he tried to carry on with his life, staying out of galactic affairs. The Sith ruled the Empire, both in the form of the Emperor himself and his enforcer, Darth Vader. One day he met a Jedi on Tatooine. He almost didn't believe it. The first thing he asked was what had become of his friend. The Jedi didn't know, but said he would do everything in his power to find out. He had a friend of his own, a callow youth, who he hoped would one day become a Jedi, too. Chewbacca was dubious until he realized the opportunity that sat before him. He was among the select few who knew that Darth Vader was this boy's father. Telling the Jedi his story, Chewbacca expressed the hope that Yoda might use this as an opportunity for redemption, after his great failure to believe the Sith had not been eliminated all those years ago.
They never saw each other again. Yoda was dead by the time Vader's son was ready to confront him and end the threat of the Sith. Chewbacca realized he'd been wrong, too, that he had given up on his friend in his moment of greatest need. It wasn't enough to save his life. But at least they had, together if apart, defeated the worst enemy they had known in their long lives.