Doctor Octopus is Otto Octavius.
He is a mad scientist who was working on an experiment involving artificial energy, when that experiment exploded. The explosion fused the four mechanical tentacle he was working with to the back of his body. This caused him to go insane and become Doctor Octopus.
The tentacles are very strong and have an array of weapons. Octopus is also very intelligent.
Doctor Octopus is a member of the Sinister Six, a group dedicated to kill Spider-Man.
Doc Ock is, along with The Green Goblin and Venom, considered to be one of Spider-Man's top three deadliest enemies.