El Sombrero was created by writer Grant Morisson.
A long time foe of the Argentinian hero called the Gaucho who specialized in making elaborate death traps for money. He often leaves a calling card consisting of a card with a skull masked in a luchador mask capped in a sombrero at his traps. During the Club of Heroes reunion, John Mayhew posed as him before being unmasked.
Later during Batman RIP, El Sombrero appears as a member of the real Club of Villains. He booby traps Wayne Manor making it impenetrable to outside forces during its occupation. Jim Gordon narrowly avoids being killed in the manor during this period before escaping the manor alongside Talia and Damian.
Sombrero also booby traps Arkham Asylum, the base of the Black Glove at the time. While scouting the location, he is attacked and apparently killed by the Joker, who poses the question, 'What is it about sombreros? Some things are just naturally funny.' He is then hung with a noose and knocked through a skylight, landing on the table used by the Black Glove.
However, a now wheelchair-bound El Sombrero returns alongside fellow Black Glove member Scorpiana and catches both Batman and Gaucho in another of his infamous death-traps. One of the heroes must die or three blind Argentinian orphans drown in a vat of sewage. A fight however does break out over the death of Kathy Kane (because both men loved her, but Gaucho killed her during his stint as Agent-33 of Spyral ). Batman manages to disable El Sombrero's security system during the melee, stop the fight and the children are saved. Scorpiana then abandons a now helpless El Sombrero to Batman. It is revealed in this scene that Scorpiana and El Sombrero were once lovers.
When Batman and Gaucho forcibly question him on who he works for, the only answer he gave was, 'the greatest of them all...' which he proceeds to laugh about. It later on turns out he has helping Leviathan.