Juan-Carlos Sánchez was trained his entire life by his father Marcus Estrada de la García to be the next in a long line of El Muertos, masked wrestlers who wore mystical masks that granted them power. But Sánchez never wanted to be El Muerto and refused to fight El Dorado as part of a ritual for the mask. As punishment, El Dorado attempted to kill Sánchez. De la García tried to stop El Dorado, costing him his life. However, his bravery earned Sánchez ten years to train. At the end of that time, Sánchez (now accepting the El Muerto identity) would have to defeat and unmask a masked hero -- or El Dorado would come for him again.
El Muerto decided to battle Spider-Man and approached J. Jonah Jameson about setting up a wrestling match. During the match, Spider-Man inadvertently poisoned El Muerto with a stinger that accidentally sprung from his wrist. Spider-Man immediately took El Muerto to a hospital, where he recovered from the temporary paralysis caused by the poison.
However, the ten years were now over and El Dorado came to kill El Muerto. Spider-Man came to his rescue and fought El Dorado until El Muerto recovered and proved his bravery by fighting El Dorado and giving Spider-Man enough time to create a reagent that dissolved El Dorado's golden armor, leaving him vulnerable to injury. Defeated, El Dorado fled.
After passage of the United States Superhuman Registration Act (SHRA) and the ensuing superhuman Civil War in America, newly-appointed S.H.I.E.L.D. Director Tony Stark classified El Muerto as a foreign national who did not normally reside in the United States, but who had made his presence known there and thus required further monitoring.
El Muerto's mask grants him superhuman strength (optimally lifting 30 tons) and endurance.
El Muerto is a highly-skilled wrestler, extensively trained in both freestyle and shoot-style grappling. Fluent in Spanish, but speaks broken English.