The Birth: One of Spidey's earliest foes, Electro had his birth way back in Spider-Man #9. Electric lineman; Max Dillon was working on an electric pole when he was struck by lightning. Through a freak of fate, instead of being fried to a crisp, his body was charged with electricity. Apparently he had been grasping the electric wires in such a way that the two bolts of current cancelled each other and the rest was history.
Max didn't find out 'bout his power untill later on when some clothes hangers got tangled around his arm and his fingers suddenly sparked.
Drunk on his new-found power, he practiced hard at throwing electric bolts and other such stuff. He even equipped his house like an electricity lab and built giant recharging poles to recharge and increase his power.
Being a mere lineman on a meagre salary, he soon ran out of dough. That's when Max Dillon decided to disguie himself as Electro and resort to looting. Man, that's a real crummy excuse to turn to crime.

The Alter Ego: Max Dillon worked with the State Electric Company as a lineman. A small job, but he was the best in his line of work. But the guy had a serious attitude problem. He cared about no-one but himself and wasn't willing to lend a helping hand to those who needed it. Naturally, he had hardly any friends. There was a time when Max's collegue; Harris was in real deep trouble on a high tension pole. It was only when Max's boss threw in a bonus of a hundred bucks that Max agreed to help.

The Legend: An armored car with a gold shipment was Electro's first target. The security guards were hardly a challenge. He then went after the Forest Hills Bank money, in the process stealing Jonah .J. Jameson's cash. Apparently J.J.J got steamed up accused Electro of being everyone's friendly neighborhood Spider-Man. When Spidey showed up to tackle Electro, he had no idea of what he got himself into. Electro knocked the web-crawler out with one bolt of electricity. He then went after the criminals awaiting transfer from the Westside House Of Detention. Now confident of his succes, Electro thought it be best if he form a gang and get these criminals to become his flunkies. Of course, good always triumphs over evil, so in the rematch Spidey easily put one over Electro.
To get revenge on Spider-Man, he joined the Sinister Six. After that he's gone team-hopping to almost every group that's formed along the way and has been recognized as a good team player. Electro has also had memberships in the Frightful Four and teamed up with various villains like Shocker, the original Blizzard, Hobgoblin and Doctor Octopus. He even formed his own team titled The Emissaries of Evil to get even with Daredevil. More recently, Electro reorganized the Sinister Six to form the Sinister Seven to hunt dowm the villain Kaine who had killed Dr.Octopus and also the Grimhunter, who had tried to kill Electro and Mysterio.
In the "Light Up the Night" trilogy Electro was feeling real down that he acutally attempted suicide and blackout NYC to prove his self worth. - one less criminal to bother about. But being the humanitarian that he is, Spidey talked Electro out of it and thought that he succeeded in reforming Electro. But the criminal reared his ugly mask again in Funeral for an Octopus.
... Besides the electrical bolts he can spew from the tips of his fingers and the recharging ability of his body, he can also traverse paths powered by electricity and construct his own mid-air electrical bridges as a mode of transport. Electro can override any electrically-powered device.

Amazing Spider-Man #9