The Bike thief (born April 12, 1970 - April 24, 2004) broke through Fry's bike chain and stole the bike on New Year's Eve 1999 while Fry was making a delivery to Applied Cryogenics, although Fry never found out because he was frozen for 1000 years.
Trivia
In the animatic for Space Pilot 3000, Fry says "hey, someone stole my bike" as he looks down on the street after having been frozen for a thousand years.