Trod

The Trods were a race of cone-shaped robots that ran on static electricity. They were native to Trodos.

In 2066, the Trods had conquered and enslaved the Human population on Trodos. When the Doctor, John and Gillian arrived on the planet, they were captured by the Trods, but escaped and defeated them. (TVC: The Trodos Tyranny)

Some time later, the Trods were reactivated by another space traveller who took control of them and used them to capture the Doctor, John and Gillian. (TVC: Return of the Trods)

Dr Who and Jason failed to prevent the Trods from destroying Arcalis. (NA: Head Games)

The Trods constructed their own space-time machine and pursued the Doctor, John and Gillian to prehistoric Earth, where they were once again defeated. (TVC: Pursued by the Trods)

Centuries later, the Doctor returned to Trodos to make peace with the Trods, but found that the Daleks had massacred them. He, John and Gillian contacted the surviving Trods and joined forces with them to defeat the Daleks. (TVC: The Trodos Ambush)

Behind the Scenes
The Trods were created for the TV Comic strip as surrogate Daleks, since the real thing could not be used at that time for contractual reasons.