[2] Castillo was born in Nuevo Valle de Moreno, a small town in the municipality of León, Guanajuato, Mexico.
He made his professional debut on 26 April 1962 against Carlos Navarrete, suffering his first loss by a decision after six rounds.
The fight was held on 6 December 1968 at the Forum in Inglewood, where Rose won a very unpopular fifteen-round decision in front of a decidedly pro-Castillo crowd, causing a riot.
He beat future world champion Rafael Herrera to defend his Mexican title, had a ten-round draw in Tokyo with Ushiwakamaru Harada, drew with Medel, and split two decisions with Raul Cruz.
He lost to former or future world champions Enrique Pinder, Bobby Chacon, and Danny "Little Red" Lopez.