A supposed time traveler from the year 2036. He first showed up posting on web boards on November 2nd, 2000, posting under the name Timetravel_0.
When questioned, he posted pictures of his time machine and its instruction manual, as well as his time traveling unit badge. Further questions yielded this information:
He traveled first back to 1975 to retrieve a particular IBM model portable computer, the 5100, which will be needed by his society to retrofit computers when UNIX code fails in 2038. John Titor acquired the 5100 from his grandfather, an IBM engineer in Rochester, Minnesota. He then time-traveled from 1975 to the year 2000, where he visited his parents (and his three-year-old self) in Florida, wrote voluminous Internet postings, and exchanged views with many other citizens of the ’Net. John Titor’s postings ceased in March 24th, 2001, when he said he would return to his own time. He has not been heard from, on what he called our worldline, since.
Among his predictions, ranging from political to absurd, is a chilling description of the great war, supposedly set to begin in 2005 after an inflammatory American election spurns a second civil war. This continues, he said, until 2015, when the third world war breaks out and the world is transformed into a postnuclear hellhole due to Global Thermonuclear War.
Supposedly, John set up relations with a woman named Pamela, to whom he told more information. She has posted on and off on web boards across the internet. In order to make sure further posts aren't made by imposters, but by Titor himself, websites suggest asking imposters about a special song that Pamela and John often talked about.
This is most likely a hoax created by a very brilliant individual or group who was well read on current scientific ideas regarding time travel and general scientific knowledge.