The Sinister Six are a group of supervillains, mostly drawn from Spider-Man's rogues gallery.
After the Justice League repeatedly foiled his criminal operations, the Kingpin realized the need of a similar group of special individuals with abilities and powers to serve as a countermeasure against the heroes. The Kingpin recruited Doctor Octopus, Rhino, Scorpion, Shocker, Mysterio, and Kraven the Hunter, whom the latter was recently bailed from prison and his genetics augmented, to form this group.
The Six began their first task in stealing Lex Luthor's newest battlesuit the Lexo-Skel 3000. The six villains worked alongside with mercenary John Corben and his men, in which the Six battled the Justice League and Spider-Man while Corben steals the suit. The Six were ultimately defeated by the heroes, as well with Corben at costing the loss of the Lexo-Skel to the League and the X-Men. All the members were jailed.
The Six were later broken free from prison by the Green Goblin and acted as his enforcers. However, Kraven, who had been reformed, decided not to escape and effectively left the Six. Instead, John Corben, having been transferred his mind to a robot body and became known as Metallo, filled in as Kraven's replacement. The Six again clashed with the Justice League and some members of the X-Men, but despite the Goblin temporarily blackmailing Spider-Man to assist them by threatening his loved ones, once the threat was removed, the Six were similarly subdued and taken back to the authorities. The Martian Manhunter also erased the Goblin's memory of Spider-Man's true identity.
In Marvel Comics, the Sinister Six were exclusively drawn from Spider-Man's rogues gallery. The original incarnation of the group was organized by Doctor Octopus.