Which of the Doctor Who production team of the time thought of regeneration is long forgotten, but it was when William Hartnell told them that after three seasons and with worsening health he needed to bow out. At that point most TV series focussed on a single character would be finished. Not so Doctor Who. Because the idea of regeneration was invented to explain it. Later it was stated that there WAS a finite number of times this could happen, and since we are up to the ninth regeneration, and the Tenth Doctor now, with the Eleventh looing on the horizon, the possibility that he could one day be no more is one fans think of more and more. But let’s go back and look at how it all happened.