Trod

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

History
In 2066, the Trods had conquered and enslaved the human population on Trodos. When the First 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 Second Doctor, John and Gillian to prehistoric Earth, where they were once again defeated. (TVC: Pursued by the Trods)

Centuries after the first encounter, the Doctor returned to Trodos to make peace with the Trods. The Daleks found out about this meeting, massacred the Trods, and waited to ambush the Doctor when he arrived. The Doctor, John and Gillian found the surviving Trods and joined forces with them to battle the Daleks. This allowed the Doctor and his grandchildren to escape in the TARDIS, but it seems likely the remaining Trods were exterminated. (TVC: The Trodos Ambush)

Hollow models of the Trods were once on display in a museum. They were marked as "Space warmongers for generations", implying they had a wider history outside of fighting the Doctor. (TVC: The Time Museum)

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.
 * Their appearance as empty shells in The Time Museum is an obvious parody of a Dalek shell appearance in The Space Museum and Pursued by the Trods is an eerily similar plot to The Chase.