M is for... Macra

Macra were giant crab-like creatures which the Doctor first encountered on a planet on which an Earth colony had been established. They dwelt underground, only emerging onto the surface at night. They had managed to gain mental control over the colony's ruler - known as the Pilot - and through him established power over everyone else. Colonists were subjected to mental conditioning as they slept, which compelled them to work for the creatures - mining a toxic gas on which they thrived. An artificial state of happiness was imposed over the entire colony. Everyone was conditioned to believe that the Macra did not exist, other than a few individuals like the miner Medok who were immune to the mental manipulation. Even the Doctor's companion Ben fell under their malign influence. 

The Doctor eventually managed to convince the leader of the colony - the Co-Pilot - of the truth of their situation, and Ben's conditioning also began to break down. The gas pumping machinery was put into reverse by Ben and the resulting explosion destroyed the Macra.

In the far, far future, around the year 5 Billion, the Doctor made a return visit to the planet New Earth. His companion Martha was abducted and taken onto the motorway beneath New New York. This enclosed space had a toxic atmosphere from the millions of vehicles trapped there, and this was being exploited by Macra living on the motorway floor. So far into the future, the creatures had devolved and were now simply ravenous animals - capturing vehicles which ventured into their reach and consuming the occupants. These were physically much larger, with enlarged claws. The Doctor claimed that Macra had been a widespread species in the past.

Voiced by: Denis Goacher. Appearances: The Macra Terror (1967), Gridlock (2007).

• A single Macra prop was constructed by Shawcraft Models. It was so large it needed to be moved around on the back of a van. With just the one prop available, scenes involving several involved it being filmed from different angles which were then mixed together. Brown in colour, it was repainted white for the final episode to act as the Control Macra.
• A separate Macra claw was required earlier, to be seen at the conclusion of The Moonbase on the TARDIS time-scanner.
• Until their return in 2007, fans were unhappy with The Macra Terror as it appeared to show the Doctor committing genocide.
• Needing a monster for the motorway, Russell T Davies at first thought of an insect or reptile but then considered that New New York sat on a promontory with sea on three sides, and so decided on a water-based creature. With the Macra already existing he simply used them, but had them devolved to become savage monsters.