He appears to be extremely good natured and friendly. However, he can be very loud and silly. He mentions a distaste for white wine preferring British sherry. He had a good relationship with his nieces, and gains the friendship of O'Malley, Duchess, and the kittens. Since he was never seen in a sober state, it is unknown just how much of his personality was influenced by his inebriated state.
Uncle Waldo first appears as Duchess, O'Malley, the kittens, and Abigail Gabble and Amelia Gabble are returning to Paris. As the group passes by a restaurant, Waldo comes flying out. The twins reveal the goose to be their uncle, and immediately notice that his tail feathers are gone. Waldo leads the group to a menu on display. The menu reveals the dinner special to be "Prime Country Goose a la Provencale, stuffed with chestnuts and basted in white wine." Waldo apparently had the misfortune of being the intended meal before escaping the chef. Waldo notes that, being British, he would have rather been basted in Sherry. O'Malley remarks that he must have been marinated rather than basted, as the goose is visibly drunk.
Waldo then begins getting very loud, so his nieces say goodbye to the cats, and begin leading him away home to bed. As they leave, O'Malley and Duchess both note that they like him, especially when he's marinated. Waldo appears at the end again with his twin nieces in Madame's mansion, where he is still drunk and sings "Everybody Wants to Be a Cat".
He made a cameo inside Fezziwig's, clapping his hands to the beat of the music. For some reason, here, Uncle Waldo appears to be more anthropomorphized than in The Aristocats, since he is actually shown wearing more clothing than just his hat.
Uncle Waldo was the last animated character that Bill Thompson ever voiced. Thompson died of a heart attack at the young age of 58 in 1971, a year after The Aristocats was released.