Amazing Spider-Man #3 (1963), the first appearance of Doctor Octopus. Art by Steve Ditko
Doctor Octopus (Otto Octavius) is a comic book supervillain in the Marvel Comics universe and is one of the greatest enemies of Spider-Man.
"Doc Ock", as Spider-Man often calls him, has a harness with four super-strong mechanical arms, originally developed to assist him in his scientific research. In an accident, the apparatus became fused to his body, and he gained the ability to control the movement of the arms using his thoughts alone. The accident also drove him mad, and he turned to a life of crime. Later, the harness was surgically removed, but he was still able to control it mentally, even at a distance. While wearing the harness, the arms are powerful enough to allow him to walk up sheer concrete walls and move quickly about. Each tentacle can lift approximately 3 tons when it has backup from another one of his tentacles. He has possessed a total of three different harnesses during his career: the original titanium harness, a more powerful adamantium harness, and the current harness, which was modified in 2004 to resemble the version seen in Spider-Man 2. The original and adamantium harnesses were both destroyed in the Lethal Foes of Spider-Man miniseries.
Doctor Octopus first appeared in The Amazing Spider-Man #3 (1963), and quickly became one of the web-slinger's most notorious foes. After the apparent death of Spider-Man's arch-nemesis, the Green Goblin, Doctor Octopus became Spider-Man's greatest foe.
Though Doctor Octopus himself is not much to speak of physically, and is near-sighted to the extent that he is legally blind without the aid of his eye-glasses, with his harness attached he is physically 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.
Despite the obvious obstacles, Octavius was for a time on good terms with Peter Parker's Aunt May, who he first met in The Amazing Spider-Man Annual #1 (1964) when he abducted her and Peter's then-girlfriend Betty Brant to attract Spider-Man's attention. In fact, in later years May Parker and Otto Octavius were briefly engaged to be married, during a period when the latter's madness had been cured (temporarily, as it turned out). It turned out that his real motive behind marrying May was to gain control a large nuclear plant that she had inherited. The plant was destroyed, however, and the engagement was called off.
Doctor Octopus is portrayed by Alfred Molina in the film Spider-Man 2 (2004). However, the story is very contracted, and Octavius seems to have become Dr. Octopus and died within a year. Another difference is that in the movie, Otto Octavius isn't really evil, but his mind is partially controlled by his robotic tentacles.