Little Mule is Granpapi Rivera's pet donkey who came along with Grandpapi when he moved in with Manny and Rodolfo. The Little Mule spends a lot of time doing donkey things and is protective of Grandpapi as seen in Puma Licito when Manny and Frida tried to retrieve his hat while he was sleeping. Little Mule has a sombrero-shaped chew toy with picture of him, his parrot brother Señor Chapi, and the Riveras.
It can be implied that Granpapi stole Little Mule from his natural habitat, and adopted him to live at his evil headquarters.
When you're selecting an El Tigre character for your NickPage on Nick.com, Little Mule was misnamed as Zebra Donkey.
Little Mule is very good at balancing stuff on his ears, like soccerballs.