Atheism was the belief in the non-existence of a god or gods.
The First Doctor told Galileo Galilei that he was an agnostic and fully expected to be an atheist by the end of his travels. (PROSE: The Empire of Glass) The Seventh Doctor later said that he had "abjured religion". (PROSE: All-Consuming Fire) The Ninth Doctor spoke disparagingly of humanity's willingness to "believe in something invisible". (TV: Aliens of London)
Sarah Jane Smith was an atheist. (AUDIO: Dreamland) While drinking in a beer tent on the planet Crex, Bernice Summerfield asserted, "There is not a God!" (PROSE: Human Nature) As Lady President of Gallifrey, Romana II commented, "There are no gods". (AUDIO: Neverland) River Song commented to a Roman commander, "You've been a soldier too long to believe there are gods watching over us." (TV: The Pandorica Opens) When he was five years old, Skagra decided that God did not exist. (PROSE: Shada)
The people of Elbyon were unable to conceive of gods or an afterlife because to do so would have been extremely dangerous in the presence of the planet's "magic" technology. (PROSE: The Sorcerer's Apprentice)
Behind the scenes
Various Doctor Who writers and actors have been self-identified atheists, including Dave Stone, Russell T Davies, Mark Gatiss and Sylvester McCoy. Douglas Adams described himself as a "radical atheist". Biologist Richard Dawkins, who made a cameo appearance as himself in TV: The Stolen Earth, is an extremely well-known advocate for and writer on atheism.