Galileo Galilei was an Italian mathematician, astronomer, and philosopher.
In 1609, Galileo was in Venice to show the Doge his telescope when he encountered the First Doctor, Steven Taylor, and Vicki Pallister, who had come to Venice responding to a mysterious invitation. Since the Doctor required Galileo's assistance at the same time he was scheduled to demonstrate the invention, Steven had to impersonate Galileo by means of a holographic disguise. The Doctor also helped Galileo improve his telescope design. (PROSE: The Empire of Glass)
The Eighth Doctor met Galileo later in his life, after he had lost his sight. (AUDIO: The Galileo Trap) Galileo later saw the effects of the Eleven's stellar manipulator on the sun, believing it to be the end of the world. (AUDIO: The Satanic Mill)