Mechanoid

Mechonoids were large spherical robots originally built by humans to help colonise worlds until they were abandoned and forgotten on Mechanus. The Mechonoids became a force in their own right and Mechanus became their home planet. They were the enemies of the Daleks.

History
The Mechonoids first encountered the Daleks when they built a space station for refuelling on the route to the planet Oric. The Mechonoids used their suspicion ray on one of the Daleks there, causing it to perceive other Daleks as its enemies and kill them. The Mechanoid Interceptor which held the ray was destroyed by the Daleks, but the Dalek ship was then attacked and melted by two other Mechonoid ships. The Mechanoids then broadcast a message to the Daleks on Skaro, warning them to avoid their territory. The Daleks instead began preparing for war with the Mechonoids. (TV21: Eve of War)

The Zerovians, seeking to prevent war from breaking out between the Daleks and the Mechonoids, sent their robot agent, 2K, to accomplish this. The robot manipulated the Daleks into destroying the rogue planet Skardal, which they had set on a collision course with Mechanus, then told the Mechonoids that the Daleks had saved them purposely. The Mechonoids then called off the war, although they still considered the Daleks their enemies. (TV21: Impasse)

Some Mechonoids were sent by humans to prepare Mechanus for colonisation, but Earth got caught up in an interplanetary war and the colonists never arrived. Steven Taylor crashlanded on Mechanus and was taken prisoner by the Mechonoids. The Daleks followed the Doctor's TARDIS to Mechanus and battled the Mechonoids. (DW: The Chase)

The Daleks later fought Mechonoids on Hesperus. (EDA: War of the Daleks)

On Lethe, Davros combined organic tissue with Mechonoid shells to create Juggernauts. (BFA: The Juggernauts)

The Mechonoids last stronghold was on Magella. The Daleks attacked and killed all the Mechonoids, making them extinct. (DWF: Birth of a Legend)

Mechonoids do not seem to be inherantly evil nor good, as they only turn violent when their home planet appears to be threatened. Otherwise, they seem to be peaceful and open to visitors; when the Doctor, along with his companions, encountered a Mechonoid, it had them follow it back to the city, and detained them to inquire about them. However, the astronaut Steven Taylor was likely kept as a prisoner because of the methods that he came to the planet - via crash landing - which possibly caused the mechonoids to consider and treat him as a terrorist agent attempting to destroy the city.

During the 41st century, Mechonoid shells were recovered from worlds ravaged by the Daleks and brought to Station 7. At some point, a Dalek force attacked the station while searching for "the Abomination", and the Mechonoid shells were destroyed along with the station. (GN: The Ony Good Dalek)

Behind the scenes

 * No explanation has been given reconciling the conflicting accounts of the Mechonoids being human servants on television and being an alien race in the comics. One theory is that when the Mechonoids were forgotten on Mechanus by the humans, they became their own race, forgetting their origins and creators. Another is that the Mechonoids lied to Steven about their origins.
 * Designer Raymond Cusick contended that the Mechonoids were originally meant to be called the "Mechons". However, the name had to be altered due to the similarity with Dan Dare's main enemy, The Mekon. (DCOM: "Day of Armageddon") Nonetheless, the Daleks do call the Mechonoids "Mechons" at one point in The Chase.
 * The Mekon later influenced the visual design of Davros. (BBC DVD: Genesis of the Daleks)