Shub-Niggurath

Shub-Niggurath was an inhabitant of the previous universe named by Rassilon. (PDA: Divided Loyalties) When that universe came to an end, she and others of her kind entered this universe, where they discovered that they were virtually omnipotent. Shub-Niggurath, who was pregnant at the time, gave birth on Polymos, thus giving rise to the Nestene Consciousness. The Sixth Doctor suggested that she died (PDA: Synthespians™) but later cited her success conquering Polymos with her offspring as embarrassing her peer, Yog-Sothoth. (MA: Millennial Rites)

A group of sentient TARDISes from the Second War in Heaven shouted "Ia Shub Niggurath!" whilst speaking with their little sister, Compassion. (EDA: The Taking of Planet 5)

Behind the scenes
Shub-Niggurath was one of the Great Old Ones created by H. P. Lovecraft. References in his work are mainly just characters shouting the name for no discernible reason. Worshipped on Earth and Yuggoth, her cult is apparently connected with fecundity, which would make her grandchildren, the Autons, her "thousand young".