They are notably the villains responsible for the death of Ianto Jones, a member of Torchwood and Captain Jack Harkness's lover.
The Ambassador was played by Simon Poland.
The 456 first made contact by radio on the wavelength sometime during or prior to 1965. The 456 had learned English and knew something of Earth culture.
In 1965, Andrew Staines, Ellen Hunt, Michael Sanders, and Jack Harkness executed a deal with the unseen aliens. In exchange for twelve human children, the 456 gave them an anti-virus for a mutated strain of Spanish influenza, which would otherwise, according to the aliens, have killed millions. These projections were agreed to by British analysts. The 456 claimed that the children would not be harmed, and in fact "would live forever" and that the 456 would not return to Earth.
Twelve orphans were taken from the Holly Tree Lodge orphanage under the pretence that they were to go to another orphanage called Harbour Heights. These children were brought to a location in Scotland, where they were ushered into a white light. For unknown reasons, the 456 decided to leave behind one orphan, Clem McDonald, who ran off alone into the night. Torchwood Three later speculated that they weren't interested in him because he was on the brink of puberty.
In September 2009, the 456 sent a message through every child—ages five to eleven—on the planet: "We are coming." They followed with detailed instructions sent secretly to Dekker for a purpose built, gas filled chamber to be constructed for them on Floor 13, the top level of Thames House, MI5's headquarters in London and the most secure building in Britain. Technicians set about constructing the containment facility before the aliens' arrival.
- The 456 are easily one of the most despicable villains in Doctor Who history. They incorporate human children into their physiology, keeping them eternally alive, childlike and fully aware. They also demanded no less than 10% of the children of Earth and turned down any compromise that John Frobisher gave them, threatening to wipe out their entire species if they didn't cooperate. When Jack and Ianto bluntly informed them that they wouldn't be getting any children, they released a virus that killed everyone in the MI5 building (excluding Dekker and Jack, but including Ianto) just to provide a demonstration of war. Worst of all, they show complete apathy towards all of these crimes and are permanently fixated on acquiring the children they desired.