Theodor Holm Nelson, born 1937, obtained his BA in philosophy from Swarthmore College. In 1960, he was a masters student in sociology at Harvard. Shortly after enrolling in a computer course for the humanities, he was struck by a vision of what could be. For his term project, he attempted to devise a text-handling system which would allow writers to revise, compare, and undo their work easily. Considering that he was writing in Assembler language on a mainframe, in the days before "word processing" had been invented, it was not surprising that his attempt fell short of completion. Five years later, he gave his first paper at the annual conference of the Association of Computing Machinery (ACM). It was around this time that he coined the term "hypertext."
Since that date, Nelson has been pursuing his dream, a software framework he named Xanadu, after Coleridge's Kubla Khan (he came up with the name while working for a publisher). This he describes at length in Literary Machines, calling it a "magic place of literary memory" (1/30).
The Xanadu software is as mythic as the place after which it was named. In Dream Machines, published in 1974, Nelson announced that it would be ready for release by 1976 (56). In the 1987 edition of Literary Machines, the due date was 1988 (0/5). The development of Xanadu was given a large boost in early 1988 when Autodesk (the company which made their fortune from AutoCAD) bought the Xanadu Operating Company. Code for a prototype of part of the system was made public later that year. In an article published in Byte in January 1988, Nelson expected to be fully completed by 1991 (299). Then, nothing. Autodesk has since relinquished interest in Xanadu.
Despite Nelson's unwavering optimism, Xanadu has failed to materialize. Nonetheless, its intellectual presence has exerted an enormous force on the evolution of hypertext systems. Few researchers would deny the influence of his ideas.
update: Recently, there have been rumours of Xanadu Light, a hypertext system incorporating at least some of Nelson's concepts. Whether this sees the "light" of day or not is irrelevant; the World Wide Web embodies many of these ideas, and is available here and now.