Monday timewaster.
It doesn't bode well for my frame of mind that I'm posting a timewaster this early on in the week.
Regardless, here it is: The Internet Surname Database.
According to them, Roy: "...is from the word rey or roi, meaning a king or chief, and in medieval times was used as a nickname either for one who behaved in a regal fashion, or who had earned the title in some contest of skill, or more likely had been elected "king for the day" in a local festival."
I already knew the 'king' part, of course, but I love the idea that the name could have been passed down simply because I had an ancestor who acted like Vanity Smurf.