Before his transformation into the megalomaniacal archenemy of the web-slinger, Otto was a brilliant and respected nuclear physicist, inventor, and lecturer. He became the youngest person to serve on the National Board of Nuclear Science. He designed a set of highly advanced mechanical arms to assist him with his research into atomic physics. The tentacled arms were resistant to radiation and were capable of great strength and highly precise movement. They were attached to a harness that fit around his body.
During an accidental radiation leak that ended in an explosion, the apparatus became fused to Octavius' body. It was later revealed that the radiation (or possibly his own latent mutation) had mutated his brain so that he could control the movement of the arms using his thoughts alone. The tentacles have since been surgically removed from his body, although Octavius retains the power to control them telepathically from a great distance. The accident also seemingly damaged his brain (although it was later suggested that what was interpreted as brain damage was in fact his mind rewiring itself to accommodate four extra limbs), and the scientist turned to a life of crime.
Though Doctor Octopus himself tends to be portly, and in poor physical shape, he has recently been able to improve upon his physique. He was also near-sighted to the extent that he was legally blind without the aid of his extremely thick eyeglasses, but he no longer appears to suffer from that problem, presumably through the use of laser surgery. With his harness attached he is physically far more than a match for Spider-Man; in his first appearance he beat Spider-Man so badly that the wall-crawler considered giving up his heroic career until he was inspired to continue by the Human Torch at the time when the Fantastic Four was called in to fight Doctor Octopus.Over the years Dr. Octopus has become one of, if not the, most identifiable member of Spider-Man's rogues' gallery.Black Cat, who was placed in critical condition and led to Spider-Man beating Doc Ock to an inch of his life. The trauma of the beating he received from Spider-Man left Octavius so afraid of Spider-Man and spiders in general for years, until Spider-Man was forced to let his nemesis beat him in combat so as to allow his nemesis to break free of his fears and recruit him to save New York City from an exploding nuclear reactor.
Doctor Octopus has worked with other supervillains on several occasions, most notably as the leader of the original incarnation of the Sinister Six. He has been a member of other versions of the Sinister Six, and founded his own short-lived version of the Masters of Evil when his teammates from the Sinister Six proved too difficult to manipulate. Certain members of the Six have since attempted to murder him, to no avail.
At one point, a boy named Oliver Osnick ran away from home, having stolen his father's Octopus-like equipment. He intended to become Doctor Octopus' sidekick, which was to be very much ill-fated. After a brief skirmish with Spider-Man, Osnick was returned home, sans tentacles.
Doctor Octopus was murdered by the insane Peter Parker clone named Kaine. Octavus's student Carolyn Trainer took over as Doctor Octopus #3, until the original was resurrected by a branch of the mystical ninja cult known as the Hand. Although Octavius had discovered Peter Parker's dual identity shortly prior to his death while curing Parker of a lethal virus created by the Vulture, he lost all knowledge of it upon his resurrection. The reason for this was the memories he gained came from a computer chip provided by his associate Carolyn Trainer with his recorded memories. That recent memory had not been recorded at the time of his death. (It is as yet uncertain whether or not Trainer had some ulterior motive for basically remodeling Octavius' mind. She bears watching.)
In recent years, Octavius attempted to create his own personal assassin in the form of a villainous mutated entity he dubbed "Spider-Woman", and was involved in a plot involving using prosthetic limbs as mind-control devices, to create an army of minions. He has also had to deal with another usurper, in the form of an arrogant-yet-brilliant scientist named Carlyle, who created his own version of Octavius' harness and who tried to kill Octavius, whose power he envied. As far as is recorded, none of the three replacement Doc Ocks are currently active, either due to retirement, jail sentences, or, in Oliver Osnick's case, deciding to emulate Spider-Man instead.
Recently, Octavius resurfaced in the attempt to kidnap a Palestinian ambassador, in hopes of causing chaos for reasons unknown. His plot was thwarted by Spider-Man and his temporary sidekick the Kiwi Kid. Octavius is currently spending time in a penitentiary.