He sacrificed himself to save Anakin Solo on Sernpidal.
At the start of the war with the Yuuzhan Vong, before the galaxy even knew of the enemy they would soon be facing, the Millenial Falcon was on Sernipdal to pick up a shipment. Sernipdal’s moon was falling, actually being pulled down by a Vong lifeform that manipulates gravity. The Falcon was being loaded with evacuees and Anakin Solo was hit by a blast of wind taking him away from the ship. Chewy chases Anakin down, scoops him up, and rushes back to the Falcon. He’s just able to get Anakin into the ship when another shockwave hits, knocking Chewy away from the Falcon. With no time left, Han is forced to take off or lose everyone on board. Chewbacca understands and as a last defiant act he throws his arms wide and bellows out a might rookie roar.

Chewbacca’s death hit me damn hard when I read that book. Recalling it now to write this even brought tears to my eyes. A hero so noble and mighty it took a moon to defeat him.

Anakin’s death later in the same series was pretty awesome but not as wrenching emotionally.