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)
He told him he should remain quiet about some of his ideas that would be seen as heretical. (AUDIO: The Galileo Trap)