William Hartnell died on April 23, 1975 at the age of 67.
William Orange died on 1966-06-28.
William Carey Graves died in 1966.
William Van Vleck died on May 19, 1966, in Los Angeles, California, USA.
Beresford Williams died on April 22, 1966.
William Edward Petty Hartnell died in 1854.
William Hartnell died on April 23, 1975 at the age of 67.
When the eleventh doctor was about to die he went past the limit of regenerations. What if William Hartnell did the same and just forgot, which is a common side effect of regenerating. So when Tom Baker had a mind battle maybe he was just remembering what had been forgotten. But there are also several pages where the doctor talks about himself as the first. So nobody truly knows.
The first Doctor died at the end of the last episode of the serial The Tenth Planet. He apparently died of old age as his body just "gave out". He staggered into the control room of the Tardis and collapsed next to the console, at which point his regeneration started.
Tim Hartnell died in 1991.
William Eerdmans died in 1966.
William Elsey died in 1966.
William Dillon died in 1966.
William Harrigan died in 1966.
William Batt - doctor - died in 1812.
William Parry - doctor - died in 1585.
William G. Pickrel died in 1966.