Thumpers, characterized by their eight legs and furry bodies, were rodents that naturally occurred on Yavin.
Not long after Biggs, along with Windy, Luke Skywalker, Han Solo, Artwo, and Threepio, got to the Wookiee settlement, Biggs captured a thumper and put it on a leash. He decided to name the creature Amber, in honor of his bodyguard.