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, said to have first manifested in this universe in the Arcturus system and to have once been worshipped by the inhabitants of a lost city in Burma, which would explain its stated familiarity with Earth. (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).