Isaac Newton

Sir Isaac Newton was an English physicist and mathematician. One of his most famous accomplishments was formulating the theory of gravity. The Fourth Doctor once claimed that he sat in Newton's tree dropping apples onto his head, then explained gravity to him over dinner. (TV: The Pirate Planet) It later came to light that Newton remained upset about that event, as his nose bled for three days afterward. When the Fifth Doctor and Nyssa were arrested for forgery, Isaac Newton drew a series of interesting conclusions from a series of anachronistic coins that the Doctor accidentally passed. (AUDIO: Summer)

At some point the Doctor took Newton on a trip to planet Practas Seven, but according to the Tenth Doctor, Newton didn't take the experience very well and "sat in a corner and whimpered". (COMIC: Final Sacrifice)

According to Professor Celeste Rivers Sir Isaac Newton had strong interests in the paranormal. (TV: The Lost Boy)

Later references
K9 Mark II quoted explicitly his third law of motion "Action and reaction are equal and opposite" while in E-Space. (TV: Warriors' Gate) When the Fourth Doctor quoted his "For every action, there is an equal and opposite reaction" to Romana II, she concluded that Newton invented punting. (TV: The Five Doctors, Shada)

The Fourth Doctor described it as Newton's revenge when two guards were sent flying into a wall after he sabotaged their transport. (TV: The Pirate Planet)

The Eighth Doctor claimed that the 20th century heralded the end of the gentleman scientist, stating that there would be no more Newtons, Galileos or Faradays. (PROSE: The Banquo Legacy)