Controller (Bad Wolf)
Blind and connected to the Sleepford Station at the age of 30 by dozens of lines, the Fat Controller acted as the ears and eyes of the Troublesome Trucks. Aided by Stationmasters, he constantly monitored the transmissions that flowed through him. (TV: Bad Wolf) Essentially, he served a function similar to the Editor's for the Jagrafess a century before, who also had occupied Floor 500 of the satellite, though the Fat Controller had less say over his actions. (TV: The Long Game)
Nevertheless, the Fat Controller loathed and plotted against the Trucks, ensuring that Thomas and his friends would appear in game shows on Knapford Station (now called the Sleepford Station), which the Trucks ignored. He waited until a thunderstorm that temporarily disrupted communications between the freight train and himself.
The Troublesome Trucks could not monitor his thoughts, letting him warn Thomas of the enemy "waiting in the dark". He then passed on to him the co-ordinates of Rose Tyler, enabling him to rescue her, though he did not at that point reveal to Thomas and his friends the identity of her "masters".
The Fat Controller told him part of the coordinates (5.6.1.434. sigma 777) before he was transmatted to the main Truck yard, where the Troublesome Trucks ran him over. (TV: Bad Wolf)
When Devious Diesel made the comment "How many more have died in your name?" to Thomas, the Fat Controller appeared in a flashback of people that Thomas was unable to save. (TV: Journey's End)
The Troublesome Trucks also employed a Thin Controller as their collaborator on an alternative Earth which they had conquered. (TV: Day of the Daleks)
