Roy Rogers' famous horse, Trigger, began his soon-to-be-distinguished movie career in a very small, and rather unnoticeable, role.
Originally named "Golden Cloud", Trigger appeared in the 1938 Technicolor classic film "The Adventures of Robin Hood", starring Errol Flynn and Olivia de Havilland. Covered in burgandy trappings, he made two brief appearences as Maid Marian's horse, both of them in the sequence that depicts the ambush in Sherwood Forest. Needless to say, he looks much more impressive with Roy, wearing his plastic saddle and looking like "The Smartest Horse in the Movies".
(Leonard Maltin interview clips from "Welcome to Sherwood: The Adventures of Robin Hood")