Animus

The Animus was an alien intelligence which landed on the planet Vortis. It could take over any living creature that was in contact with gold and had already taken control of the ant-like Zarbi when the First Doctor and his companions arrived on Vortis. One of Vortis' surviving lifeforms, the Optera, referred to the Animus as "Pwodarauk". The Animus manifested itself within an organic, self-healing palace called the Carcinome.

The Animus's true form was revealed, as resembling an octopus with some arachnid features. The Doctor, Ian, Barbara and Vicki helped the Menoptera to destroy the Animus using the Menoptera's secret weapon, the Isop-tope. After that, the travelers left the natives of Vortis to resolve their differences peacefully. (DW: The Web Planet)

Later, the Second Doctor, Jamie and Victoria returned to Vortis and encountered a seed of the Animus which had survived. (MA: Twilight of the Gods)

The Animus was later identified as the Great Old One Lloigor. (NA: All-Consuming Fire) There are many Lloigor but the Animus was the only one known to have been able to enter our universe. (MA: The Dark Path)

Eventually, The Greater Animus perished in the Last Great Time War, and its Carcinome Walls fell into dust. (DWA: Doctor Who Annual 2006).

Behind the scenes
Lloigor (and its twin Zhar) was created by H. P. Lovecraft's contemporary, August Derleth, who also made Hastur and the legendary Windigo into Great Old Ones. The singular reference in Doctor Who to a plural Lloigor comes from a later Colin Wilson story which suggests that the fictional Lloigor got its name from a very real group of beings.