El Dorado was created solely for the Super Friends cartoons and has never appeared in a DC Comic. He first appeared as minor character in the Super Friends animated shorts, which aired in 1981 season and later in Super Friends: The Legendary Super Powers Show as a full-time member. El Dorado spoke English with an accent, sporadically substituting common Spanish words or phrases, such as adding words like "rapido" and replacing nearly every instance of "yes" with "si".
In El Dorado's debut episode "Alien Mummy" it is revealed that he is of Mexican descent. The narrator sets the scene by describing the location as 'ancient Aztec ruins in the Mexican wilderness'. One of El Dorado's lines is "these are the mysterious ruins of my people".