John Titor is, perhaps, one of the most successful internet troll/hoax artists of all time. Not only did he get a large number of people to buy into his crap story, but he also managed to make money off it.
Sometime around 2000, some guy started posting on a message board devoted to, you guessed it, time travel, claiming to be a time traveler from teh future!!1! Normally such claims would be laughed down, and rightfully so. Internet forums, on the other hand, are hives of scum and villainy, home to the gullible, the humorless and those with no sense of reality whatsoever. As such, a considerable number of people bought into it, resulting in a good amount of lulz from those still clinging to their sanity.