Mr. and Mrs. Whipple appear in Season 15, episode The Last of the Meheecans.
Background
The Whipples hit Butters with their car while he is trying to find his way back the Eric Cartman's house. He was lost when he got separated from the other during a game of Texans vs. Mexicans.
Personality
The Whipples are very nice to Butters although they seem condescending and naive. They treat him like a servant giving him a bottle of window cleaner and making him wash the dishes. The couple buy him a gas powered leaf blower as a present. Not realizing that Butters is an American boy they take him to a El Pollo Loco restaurant "to be with his own kind."
The Whipples appear to be religious for the many Christian icons and slogans decorating their walls.