'The Mexican Cowboy' became the second boxer from his country to win a world title in four different weight divisions.
He started professional boxing at age 16, and amassed a record of 14-2.
He developed a trademark entrance involving a black cowboy hat and a lollipop.
His girlfriend was reportedly teaching him English to help him gain popularity in the U.S.
Lamon Brewster is another WBO champion, but he was in the heavyweight division, so they never fought.