Klytode

The Klytode was a powerful being who tried to destroy the Earth on three separate occasions. He was defeated on every attempt by the Tenth Doctor.

Biology
The Klytode was a gestalt being, one powerful mind with many bodies. Each Klytode shared the thoughts and ambitions of the master creature. Their homeworld, on the edge of the Aktren Galaxy, was left a dark husk of matter — a fate of any world that the Klytode inhabited. They were known to use androids to help achieve their plans. (COMIC: The Snag Finders)

History
In 3738, the Klytode attempted to destroy Earth during Christmas, but was defeated by the Doctor. (COMIC: A Klytode Christmas)

In 3769, the Tenth Doctor encountered the Klytode on Space Station Alpha, where it was planning to detonate a cobalt bomb on board the space station, sending it crashing to Earth causing a catastrophic change in the climate in readiness for the arrival of the Klytode brethren. The Doctor foiled its attempt by ejecting the bomb into space and the Klytode was arrested and sent back to the Arktren galaxy. (COMIC: The Snag Finders)

In 4041, the Doctor defeated the Klytode for a third time when it tried to destroy the Earth by releasing toxic bombs around the world's weather control centre using a delegation of androids. When the androids learned that they would be destroyed in this plan, they turned on the Klytode. The Klytode was captured and when it said it would never change its ways until the Earth was destroyed and the Doctor totally humiliated, it was left to be held under lock and key. (COMIC: Return of the Klytode)