Sprawn

Director Sprawn was the would-be governor of a human colony whose plans to destroy a native population to establish his colony were defeated by the Eleventh and Fourth Doctors. (PROSE: The Roots of Evil)

Biography
Sprawn was the head of a project to establish a human colony on a distant world. He clashed with the Doctor when his proposed terraforming event of the planet Golrandonvar threatened the local population, known as the Thara, who would be unable to breathe the new atmosphere if the terraforming was completed due to their reliance on helium. The Thara and the Doctor banished the colonists from Golrandonvar, forcing them to retreat to the Heligan Structure.

Quest for vengeance
Refusing to allow The Doctor victory, Sprawn literally merged with the roots of the Heligan Structure and a series of computers, keeping the would-be colonists trapped on the structure so that he could nurture their vow of vengeance against the Time Lord. Sprawn manipulated records to suggest that the Thara were vicious, primitive swamp-dwellers. The population came to regard The Doctor as the colony's boogeyman rather than a real person, although a select few remained dedicated to their original "goal" and their names were chosen to reinforce the vow of vengeance against the Doctor. Sprawn's long-term goal was that the Doctor, with his interest in travel and ability to travel in time, would eventually visit the Heligan Structure as it remained in space, allowing him to achieve his revenge.

The Doctor's first encounter
Although Sprawn's plan succeeded nine centuries later, it also essentially went wrong as the structure was eventually visited by the Fourth Doctor and Leela, rather than a Doctor who had experienced the events on Sprawn's original colony world. Although the Doctor created some confusion among the colonists when he acted to save a young boy even after the boy denounced him as evil, the colonists only realized that something else was going on when the Heligan Structure itself began to attack the colonists while trying to kill the Doctor, manifesting humanoid 'spores' that couldn't distinguish between humans and the Doctor.

Determining that the original colonists had been driven off by one of his future selves, the Doctor travelled down to the Structure's roots and confronted Sprawn. As the spores came at the Doctor, the Doctor used the computers around Sprawn to revert them to their original programming to spread seeds and purge the tree of parasites, prompting them to attack Sprawn, destroying him once and for all. (PROSE: The Roots of Evil)