The Birth: Quentin Beck started his life of crime way back in Amazing Spider-Man #2 but later on took on the personality of Mysterio in Amazing Spider-Man #13, 1964.

The Legend: Quentin Beck stared his career as a hollywood stuntman. Later on, he started work on the special effects team and soon became one of the industries' top special effects artists. But this backstage job was not meant for one like Beck who craved to be in the limelight.
Then one day, one of his friends jokingly mentioned that if he could take down one of the costumed heroes who seemed to be poring out of the woodwork he would instantly earn a name for himself.
That's when Quentin Beck changed and started studying the then fledging Spider_man.
Later, a villain called the Tinkerer hired him to steal industrial and military plans. The two men pooled their genius and developed an alien disguise to mask the true nature of their crime. The scheme was foiled by Spider-Man, but the hero did not see through the villains' diguises.
Beck took his defeat by Spidey sorely and adopted the image of Mysterio to battle the wall-crawler. Using hi-tech illusions and gadgets, Mysterio was still defeated by Spidey.
He then joined the Sinister Six after an invitation from Dr. Octopus
A master of illusion, Mysterio worked over-time to make the wall-crawler think he was going mad. One of his favorite tricks is making Spidey think his foes were literally coming out of the wood-work; once Mysterio did the illusion so well Spidey shredded his hands against a harmless-enough brick wall. Another time Mysterio convinced Spidey that he'd been shrunk to the size of a pin-head.
...... But each time Mysterio was hauled back to prison. Soon realization dawned on the villain that his antics were not earing money and instead were making the super-heroes mighty angry with him. So after coming of of prison one day, he changed his tactics!
To the world it looked like Quentin Beck a.k.a Mysterio had finally reformed. At least he wasn't into anything illegal. He set up a home for the aged and took care of all the old people. But he had an ulterior motive behind it. He showered so much care and concern on the rich elderly inmates that when they died they left their entire fortunes on his name. Incedently, in this new "reformed" image he went by the name of Dr. Ludwig Rinehart.
May Parker, being quite old, checked herself in Mysterio's rest home. But the "burglar" who had killed Peter's Uncle Ben, followed May Parker, still thinking that the Parker house hid some fantastic fortune. Through him, Mysterio came to know of the "fortune" and wound up finding something that had long since been devoured by the silverfish. After this, he went back to his original purpose of making Spidey doubt himslelf.
Besides Spidey, Mysterio has also gone aginst the likes of the Human Torch. He is also a prime target for the Spidey clone; Kaine. Though Spidey has cracked his fishbowl helmut umpteen times, Mysterio got really mad when Peter Parker's ex-girlfriend Deborah Whitman bopped him over the head and cracked the helmut.
...... Mysterio is a genius when it comes to gadgetry. He's used mechanical springs to "disappear," an electrically charged cape, and electronic animals. He excels in holographic devices and is also a master hypnotist, prestidigitator and a roboticist. Mysterio's illusions, which often rely in part on hypnosis, are so real they can even confuse Spidey's spider-sense at times.
The equipment he uses is a one-way plexiglass helmet with half-hour air supply & holographic projector; gas jets mounted in gloves and boots capable of emitting hallucinigenic, sense-dulling, gases. The corrosive acid he stores in his gloves comes in handy whenever there is webbing that needs to be dissolved. He occasionally carries hypnotic aides & conventional hand held weaponry.

Amazing Spider-Man #13