From Guy Fawkes probably although his name was Guido.
An effigy of Guy Fawkes was traditionally burnt on the bonfire But it�s also where guy in the sense of a person comes from. It was originally applied to a man of grotesque appearance, like a bonfire effigy, but when it was taken to the US in the late nineteenth century it turned into a neutral term for a man, more recently (in the plural) persons of either sex. It was also used for a person who acted as a dupe in a confidence game and led to the verb to guy, to ridicule or hoax.