Horrendo is a non-anthropomorphic gorilla and circus performer.
Horrendo is a wild gorilla, the property of Wild Animal Circus. He appears to not very much enjoy being a part of the circus, which binds with him chains. Despite his lack of enjoyment for it, he has been described by its manager as its star, apparently bringing in thousands of dollars per show thanks to his ferocity and strength.
Sometime in the 1960's, after breaking free from one of the circus' trucks, he had a run-in with barber Donald Duck, who did to him what any barber would do to a large hairy fellow who entered his shop. After becoming horrified at what Donald had done to him, he rushed back to the Wild Animal Circus, apparently seeing it as better than staying with Donald.
Behind the scenes
Horrendo's first and only known appearance was in Carl Barks's Spare That Hair, which was released in May of 1963. His name seems to be a play on the word "horrendous", which refers to something unpleasant or horrifying.