Electro is set to change the MCU in Spider-Man: No Way Home, thanks to the multiversal casting of Jamie Foxx from The Amazing Spider-Man 2. While the character hasn't been a huge part of the movies so far, comic book readers know that Electro has been a major Spider-Man antagonist for decades.
Maxwell Dillon is one of Spider-Man's earliest foes, and one of his most consistent antagonists. He's evolved along with Peter Parker since the 1960s, getting updates to his look and powers. And naturally with comics and soon the MCU, there are alternate versions of the character from different realities out there as well.
Electrifying Origin
Electro was similar to a lot of Spider-Man villains in the early days of the Marvel Universe in that his power came from a freak accident. Though it wasn't scientific in nature (as was the case with Doctor Octopus, for example), physics was involved. Max Dillion was hit by lightning while working on an electrical line. This transformed him into a being who could generate and control electricity. He initially had to maintain a charge, which led to him stealing electrical equipment, including advanced technology from Tony Stark.
Potential Recruit For The Brotherhood Of Evil Mutants
While not a mutant, Electro was nonetheless recruited for the Brotherhood of Evil Mutants by its leader, Magneto. At the time, Magneto was leading the team against the X-Men, fighting alongside Toad, Mastermind, Quicksilver, and the Scarlet Witch. Electro turned down Magneto since he wasn't a mutant, but he quickly launched into a career of crime. Not only did Electro steal parts and equipment to keep himself charged, but he also robbed banks and committed other petty crimes that put him on the radar of Spider-Man.
Founding Member Of The Sinister Six
Electro first appears in The Amazing Spider-Man #9 in 1964, and he quickly becomes one of Spider-Man's most important adversaries. That's cemented when he becomes a founding member of the Sinister Six, the supervillain team that assembles in The Amazing Spider-Man Annual #1 also in 1964. Electro joins forces with Doctor Octopus, Sandman, Mysterio, Vulture, and Kraven The Hunter to kidnap Betty Brandt so they can lure Spider-Man into a trap. It doesn't work out for them, but it's not the end of the team by any stretch.
The Frightful Four
The Sinister Six isn't the only supervillain team that Electro has been part of. In fact, he's been part of several. One of the most significant is the Frightful Four. Electro appears as a member of the team, which includes the Wizard and Trapster, in Spectacular Spider-Man #39.
This is a later incarnation of the Frightful Four, who originally appeared as villains of the Fantastic Four in Fantastic Four #36 in March 1965. The team originally was comprised of another Sinister Six alum, Sandman, as well as the Wizard, Paste-Pot Pete, and Medusa.
The Emissaries Of Evil
Spider-Man wasn't the only superhero that Electro targeted. He also was a frequent adversary of Daredevil and once took him on as part of the Emissaries of Evil. Electro founded this group to get revenge on Daredevil and was made up of several of the most laughable Spider-Man villains, including the Gladiator, the Matador, Stilt-Man, and Leap-Frog. The team first appears in Daredevil Annual #1 in 1967 and would go on to be a problem for Daredevil and other heroes over the years, though the roster would change quite a bit.
The Sinister Seven
Electro would be part of many other versions of the Sinister Six, including the Sinister Seven. This team appeared in the '90s and was focused on taking down Kaine, an evil clone of Peter Parker who debuted during The Clone Saga. The Clone Saga is probably a comic book crossover best avoided by the MCU given its sprawling and confusing nature, but the Sinister Seven is interesting in itself. With Kaine killing enemies of Spider-Man, the supervillains had to team up to survive.
Amplified Powers
Early on, Electro had to maintain a charge with his powers, which were considerable but limited in nature. As the years went on, he learned how to absorb and harness the latent electrical energy around him to not only stay charged but boost his power. Max Dillion then underwent an experimental procedure that upgraded his powers even more, giving him extraordinary control over electricity and nearly unlimited power. He also gained some measure of control of magnetism, perhaps fulfilling Magneto's early estimation of his potential.
Francine Frye
Many of Spider-Man's major villains have successors or imposters, like the Green Goblin or the many versions of Kraven The Hunter. Electro is no different. One of the most significant versions of the character from the main Marvel Universe of Earth-616 is Francine Frye.
Francine Frye debuted in The Amazing Spider-Man vol. 3 #2 in 2014. She was a huge fan of supervillains and Electro in particular. She has a very complicated backstory, which includes being electrocuted by Electro and then being resurrected as a clone with his powers.
The Electro-Verse
Francine isn't the only version of Electro. In fact, there are infinite versions of him. One of the most fascinating things about the character in the comics is the Electro-Verse. This is a similar concept to the Council of Kangs, in which Electro assembles and leads a network of Electros from across the multiverse. These are dozens of different Electros who all have the same powers more or less, but have different circumstances, and are sometimes different genders or are different ethnicities. All of them more or less hate Spider-Man and his infinite variations as well.
Ultimate Electro
Another major variation on Electro exists in the Ultimate Comics universe of Earth-1610. This early 2000s imprint sought to update major Marvel characters and stories for the modern-day and Electro got a revamp as well. Instead of a random accident, Max Dillion got his powers from a scientific experiment. He is also much more ruthless and effective. Whereas Electro's early comic adventures were marked by failure, his first contact with Spider-Man in this universe ends with him electrocuting and unmasking Peter Parker.