Dekker

Dekker was the head of MI5's technology division.

Early life
Dekker worked in the Civil Service and never started a family due to him being too busy working. He became head of MI5's technology division, based in a small and cramped office in which he rarely received visitors. Although they converted the 456 readings onto digital, he kept the original equipment out of nostalgia (TV: Children of Earth: Day One) and spent forty years trying to crack the transmission. (TV: Children of Earth: Day Five)

456 incident
In September 2009, Dekker informed John Frobisher that the equipment was active at the times that the children stopped, confirming that the 456 were behind it, and that he was running it through the translators. (TV: Children of Earth: Day One) Once the translations were complete, he found that they were instructions to build a tank, a project for which he called in the Damage Control Team. (TV: Children of Earth: Day Two)

Dekker was in Thames House during the conversations with the 456 ambassador. (TV: Children of Earth: Day Three) He sent a man with a camera into the tank per the 456's orders and detected the signs of a third life within, that being of one of the 1965 children. He was the only person to survive the massacre of the building, which he did by putting on a hazmat suit. (TV: Children of Earth: Day Four)

When Colonel Augustus Oduya arrived to take over negotiations, Dekker greeted him. He was knocked out and taken to Ashton Down by Johnson and her men during their breakout of Captain Jack Harkness, also being shot in the leg by Johnson when he complained. He helped Jack come to the conclusion that a child could be used to defeat the 456, but that the child would "fry". He watched and was upset by Steven Carter's death. (TV: Children of Earth: Day Five)

Personality
Dekker remarked that the reason that he kept on surviving was by stepping back. (TV: Children of Earth: Day Five) He did not hold elected officials in high regard and believed that the Civil Service were seen as the "cockroaches of government". (TV: Children of Earth: Day One)