D is for... Dekker

A government scientist, working for MI5, who was an expert on the alien race known only as the 456, as this was the radio frequency they used. He first became involved when the aliens visited Earth in the 1960's and demanded a number of children. Captain Jack Harkness helped deliver them from a children's home. Dekker continued to monitor the frequency and he alerted the government when they re-established contact in 2009. This time they planned to visit the planet in person, and Dekker was responsible for preparing a suitable habitat for them to materialise in. This time the aliens wanted thousands of children, as they used their body chemistry as a drug. When the 456 released poisonous gas into Thames House, it killed Ianto Jones, but Dekker managed to get into a biohazard suit in time to save himself. Dekker later helped devise the scheme which would repel the creatures, though he warned that this would require a child to do it - and that child would be killed. Captain Jack sacrificed his own grandson to achieve this.

Played by: Ian Gelder. Appearances: TW: Children of Earth (2009).