James Donovan Halliday (1972-2039) is the main character and tech industry celebrity in the backstory of Ready Player One. He was the creator of OASIS, a massive online simulation used by billions of people in the story's dystopian future setting. Author Ernest Cline based the magnate's personality on those of historical figures Howard Hughes and Richard Garriott.
When the story begins, the late Halliday has just willed a major prize to whosoever finds a unique, hidden easter egg in his VR realm, the OASIS. The terms of the will would give the finder his multi-billion-dollar fortune, along with administrative control over the OASIS itself.
Creator of OASIS. Described his childhood as "neglected" even though, compared to mid-21st century standards, it was incredible. A lot of inspiration for his games comes from his perceived sub-standard childhood.
James was a social outcast who had trouble talking to girls growing up, and came off as awkward and unappealing. He's thought to have been on the Autistic Spectrum with the condition once called Asperger's Syndrome.
Kira Underwood, who he called Leucosia, may have been the only female that he ever contacted in a casual, social context.
Halliday took his primary avatar's name, Anorak, from Kira.
Halliday was outwardly in love with Kira, but so were many others. He could never find the courage to ask her out. When Og married her, Halliday's dreams were crushed. Subsequently, given that James was thus smitten with Ogdon Morrow's (late) wife, he chose to break contact with Og for the rest of his life. Their love for Kira created a division between the two men.
After Parzival wins his egg hunt, Halliday admits he only realized that he only built and spent most of his time in the OASIS near the end of his life, telling Wade that he can only experience true happiness in reality. This prompts Wade to begin to relish being in the outside world more, and for the first time in his memory, realize he didn't want to go back into the OASIS.