The Diadem

The Diadem was a mind parasite that had the appearance of a tiara that was inhabited by an evil intelligence that was implied to be similar to the Keller Machine mind parasite. (NA: Legacy)

Description
The Diadem was first seen on Pakha where it possessed a Pakhar forager named Vor'r'na and plunged the native inhabitants to centuries of war with each other. However, there were some pacifists who attempted to change their society. The Doctor, with his companion, Jo Grant arrived on the planet thwarted when the mad Vor'r'na fell into a bottomless chasm, along with the diadem. The Doctor, however, doubted it was completely destroyed. (NA: Legacy)