Rotten Ralph is a series of children's picture books written by Jack Gantos and illustrated by Nicole Rubel. About twenty Rotten Ralph books have been published from 1976 to 2011. Rotten Ralph is also the first book in the series, a 32-page picture book published by Houghton Mifflin of Boston in 1976. It was the first published book for both Gantos and Rubel.

Alternatively, Rotten Ralph is the title character of the series, initially "a very very nasty cat" —a bright red domestic cat who enjoys playing mean, practical jokes on his human family.

There was a children's television series by Cosgrove Hall Films, Tooncan Productions and Italtoons Corporation based on the books, first broadcast on CBBC from 1998 to 2001. It also went to air on Nickelodeon in the UK too, around 2000. The show hasn't been aired in the UK since reruns ended in 2005. The show aired in the United States on the Fox Family Channel from 1999 to 2001.