Billy, a guard of Falador is a Falador guardsman seen during the Garden of Tranquility quest. Billy is shown to be working with another guard, named Bob, to protect Falador's northern entrance. Both are subsequently killed by PKMaster0036, a player spoof.
Billy's death allows the player to sneak a statue of Saradomin out of central Falador and unnoticed, eventually allowing them to reach Varrock Palace. They are also referenced briefly during the Ratcatchers quest, in which guards in the East Ardougne mansion occasionally say "I miss Billy and Bob," even if the player hasn't even started Garden of Tranquility.