Real Name: Maxwell Dillon
Group: Sinister Six
First Appearance: Amazing Spider-Man #9 (November, 1963)
"Jewels! Money! No matter how much I take, I want more--much more! And with my great power, nothing can stop me from getting it!" - Electro
One day another lineman got in trouble and Dillon agreed to save him, but only after the coworker would expressly remark to the electric company about Dillon's heroism, which would auger well for his chances of getting promoted. However, a freak lightning storm hit and caused the lineman in distress to lose his balance and fall to his death. In the process Max Dillon gained superpowers when he was struck by lightning while in contact with power lines still connected to their spool. The unusually configured magnetic field generated by the wound spool of cable and live, high-tension wires induced a body-wide mutagenic change to his nervous system. Dillon found himself transformed into a living electrical capacitor, powered by the micro-fine rhythmic muscle contractions that normally regulate body temperature.
Sinister Six
Unable to best the wall-crawler on his own, Electro often sought strength in numbers. Early in his career, he and five other members of Spider-Man's rogues gallery united under the leadership of Doctor Octopus - brilliant, respected scientist turned tentacled terror. The inaugural incarnation of the Sinister Six also included the shifty Sandman; the illusion-casting Mysterio; the high-flying, lowdown Vulture; and Kraven the Hunter. The villains' master plan: Pummel the wall-crawler one by one until one of them would manage to defeat him. The outcome: Spidey 6, bad guys 0.
Emissaries of Evil
After the events of The Six, Electro was hired by Doctor Doom amongst others to disrupt the wedding of Reed Richards and Susan Storm. Later he was defeated by Daredevil and sought the help of other super-villains when he created his own Emissaries of Evil.
Other Sinister Six Incarnations
Stinging from their initial failure, the Six stepped up their efforts. With the half-demon Hobgoblin standing in for Kraven, they planned to hold the world for ransom under a cloud of poison gas. Spider-Man was no match for the villains' collective might, but Dr. Octopus deserted Electro and the rest of the team when he discovered he could sell the gas as a cure for cocaine addiction. Without Doc Ock's guidance, the Six easily were dispatched by Spider-Man. A subsequent scheme to destroy their treacherous leader ended when the rudderless rogues went their separate ways after failing to achieve their objective.
Electro was also a member of Mysterio's Sinister Seven, created to combat Spider-Man's insane, homicidal clone, Kaine. However, Kaine disappeared and with no further need to keep the group together, it was disbanded, and Dillon returned to his self-imposed exile.
Superior Six
Electro returned to Earth and attempted to avenge himself on Thor by forcing an A.I.M. scientist to convert him to generate protons instead of electrons, but he was defeated when Spider-Man (actually Doctor Octopus' mind in Spider-Man's body at that time) managed to convert him into a stream of protons and trap him. Spider-Man placed Electro in a containment cell next to Sandman's in his hidden underwater lab.
Max, who had been incarcerated at Andru Correctional Facility, was broken out of the prison by Rhino, along with the Lizard, in the behest of the new Jackal, who planned to give Max his powers back.
As he was about to have his powers returned to him by the Jackal and the Lizard, Maxwell changed his mind and decided he couldn't go ahead with the procedure. The Jackal then ordered a resurrected Francine Frye (whom Dillon had accidentally killed months earlier) to appear, convincing him to proceed with it.
However, the procedure failed to give him his powers back as his body rejected them. After the failed experiment, Dillon passed by Francine and the suit began to transfer its energy to her. Francine kissed Dillon, absorbing all the energy from the suit to gain his powers, the transference killing Dillon by frying him to death.