The Puppeteer

 was a Vrund who somehow made it to Earth in the 19th century and was forced to bond with a human. The human was driven crazy by the bonding, and the Puppeteer continued to bond with humans, eventually following them on their travels into space.

Annajin Valentin tracked the Puppeteer to Gondovan, where it had possessed her brother Sukhrit. However, by this time the Puppeteer was possessing Oliver Day, and Annajin helped the Doctor defeat the Puppeteer, freeing Oliver. (PROSE: Puppeteer)