456 ambassador

The 456 Ambassador was a member of the 456, who came to Earth to extract 10% of its children for the purpose of drug-dealing and usage. The Ambassador was the only individual of the species that humanity had direct contact with.

Biography
The Ambassador had one of the twelve children from 1965 wired into its body. The 456 race extracted fluids from the brains of human children to create a sensation equivalent to drug intoxication. The Ambassador arrived in a pillar of flame and landed in a specially built tank in Thames House. It relayed its race's demands to the government and, when confronted by Jack Harkness, showed the extent of its power by releasing a toxic gas into Thames House that killed all inside.

Once the government had agreed to hand over the children, the Ambassador decided to wipe out the last remnant of the race's last visit to Earth and killed Clement MacDonald with a hypersonic sound wave. However this proved to be the Ambassador's undoing; Torchwood were able to send the same signal back at the Ambassador, seemingly killing him as bursts of his blood splattered against the inside of his container. (although his body was removed in another pillar of flame before this could be verified) It is unknown if the Ambassador was the only 456 present. (TW: Children of Earth)