Stephen Hawking
Per T:RW, this page should be moved to Steven Hawking, since that's how his name was spelled in The Tomorrow Windows.
Talk about it here.
Stephen Hawking was a human scientist and theoretical physicist in the late 20th to early 21st century.
In 1997, Hawking was among the celebrities observing the Mars 97 mission at the National Space Museum. He was in deep conversation with Richard Dawkins and his wife. (PROSE: The Dying Days)
In 2004, Hawking attended the opening of the Tomorrow Windows at Tate Modern. (PROSE: The Tomorrow Windows)
When Dalek Thay encountered the Cybermen, Mickey Smith compared their conversation to Stephen Hawking meeting the Speaking Clock. (TV: Doomsday)
Stephen Hawking died some time before 2050, where the famous scientist Alistair Gryffen used the phrase "Hawking's Ghost!" to express shock. (TV: The Last Oak Tree)
Behind the scenes
Hawking's first name is misspelled as "Steven" in The Dying Days.
Hawking was interviewed as part of Doctor Who Live: The Next Doctor.
He was also portrayed by Benedict Cumberbatch in a 2004 BBC dramatisation of his time at Cambridge University.