El Oso is a supervillain who commonly steals from banks.
El Oso is covered in tan bear fur, with black tuffs on his arms. He has a bear hat with teeth covering his head, a skull necklace, claws on his hands and feet and a metallic like belt similar to the cuffs on his arms. His fur could be a pelt from a bear he once battled.
El Oso was abandoned in the forest when he was a baby after being left behind on an orphanage camping trip. After crawling about for a while, he happened upon a family of bears that unwillingly took him in with them. He soon began to train under the influence of the bears, learning their way of life until he was a full fledged citizen of the bears (much to their annoyance). He soon fell in love with the princess of the bear kingdom, so he asked the Bear King if he could marry her, but was mauled. Not being particularly smart, he assumed the bear king couldn't let him marry her because he didn't have the money to take care of her, so he moved to Calavera with his brother bear Ossito, and began to steal from Miracle City in the hopes that he could steal enough money to please the bear king and win his true love's heart.
In Oso Solo Mio, he discovered that the bear princess had a boyfriend, but in No Boots, No Belt, No Brero it is seen that the bear princess has moved in and fallen in love with El Oso as she is in his house accepting a safe wrapped in a bow happily before he is hit by El Mal Verde.