^ Doctor Octopus is regarded as one of Spider-Man's worst enemies and archenemy. He has been cited as the man Peter might have become if he had not been raised with a sense of responsibility. He is infamous for defeating him the first time in battle and for almost marrying Peter's Aunt May. He is the core leader of the Sinister Six and has also referred himself as the "Master Planner". ("If This Be My Destiny...!") Later depictions revealed him in Peter Parker's body where he was the titular character for a while.
^ Not counting any other character in the mainstream Marvel Universe with that name. Only outside of the mainstream Spider-Man comics or in other media is there other Spider-Man villains (that isn't named Mac Gargan) that are antagonists of Spider-Man. Gargan is cited to be the fourth who is called that in the comic books but is the most iconic villain with that name.
The practice may have originated in a Celtic festival, held on 31 October–1 November, to mark the beginning of winter. It was called Samhain in Ireland, Scotland and the Isle of Man, and Calan Gaeaf in Wales, Cornwall and Brittany. The festival is believed to have pre-Christian roots. After the Christianization of Ireland in the 5th century, some of these customs may have been retained in the Christian observance of All Hallows' Eve in that region—which continued to be called Samhain/Calan Gaeaf—blending the traditions of their ancestors with Christian ones. It was seen as a liminal time, when the spirits or fairies (the Aos Sí), and the souls of the dead, could more easily come into our world. It was believed that the Aos Sí needed to be propitiated to ensure that the people and their livestock survived the winter.