Though the personal name has been around longer, 'guy' as a noun started with an attempt to assasinate King James I of England, along with all of Parliament. It became known as the "gunpowder plot". The plan had a man stationed in the cellar with a bunch of gunpowder and a very slow match, allowing him to make his escape. One of the people killed in that meeting of Paliament and the king would have been a very dear friend of one of the conspirators, and this conspirator made a bad decision to write that friend anonymously and warned him to stay away on that day. Naturally, when the friend received the warning, he started an investigation (November 4, 1605). The man in charge of lighting the powder was arrested, along with some of his co-conspirators, and all were hanged. The man whose job it was to light the powder was named Guy Fawkes, and by some strange coincidence, the English have a holiday every November 5th called Guy Fawkes Day. On that day, the English carry dummies through the streets, dressed as he was - in ragged clothing. After that holiday became accepted by the people, anybody who was dressed in ragged clothing, or at least appeared kinda ragged, became known as a "guy". Heck, that's changed quite a bit. Every man I remember in "Guys and Dolls" wore a suit.