Clement McDonald

Clement MacDonald, simply known as Clem, or Timothy White by the staff of the Digby York Hospital, was one of twelve children offered to the 456 in 1965 and the only one not to be taken in that exchange. He would grow up in secret, until Torchwood Three took notice of him when he began chanting the mass message spoken by the children of Earth in 2009. He was known as "the Remnant" by the 456, who eventually "disconnected" him, resulting in his death.

First encounter (1965)
He was born in Scotland some time in the 1950s. An orphan, he grew up at the Holly Tree Lodge in the same country. In 1965, an alien race designated the 456 came to Earth to offer the human race the anti-virus to a new strain of Spanish influenza which would wipe out millions of lives, in exchange for 12 children, to be harvested for certain chemicals that gave the 456 an equivalent of a high from Earth narcotics. The government and the Torchwood Institute chose Clem and eleven others from the orphanage, believing that that no one would miss them, and so kept the act a secret. After arriving in a secluded location, Captain Jack Harkness drove them to a white light, and guided them from there. (TW: Children of Earth: Day Four) However, Clem was the only one who managed to escape. He was chased for several miles until the 456 decided to stop. (TW: Children of Earth: Day One)

After that, he was somewhat slightly connected to the aliens, and possesed of a sense of smell far beyond normal for a human being, as well as psychic ability. For the next four decades he would be haunted by Harkness' face, (to the point where he recognised Harkness's scent years later), and was for unknown reasons submitted to a psychiactric hospital in West Sussex. He subsequently lost his Scottish accent and went under the alias of Timothy White to avoid detection by the government. (TW: Children of Earth: Day One)

Theory
Gwen theorised he was spared because he was on the cusp of puberty, which may have rendered him useless to the 456. Although they seemed to have simply abandoned him, some measure of a two-way connection did remain. (TW: Children of Earth: Day Four)

Second encounter (2009)
In September, 2009, the 456 returned and began transmitting a message through the voice of every child on Earth: "we are coming." Clem also chanted the words, the only adult known to do that too. This attracted the attention of Gwen Cooper from Torchwood Three. She took time to visit him on the first day of the 456 incident. As "Timothy White" listened to Gwen, he was able to use his sense of smell to determine she was telling the truh that she worked to stop alien threats. He told her his actual story and that he could sense the coming arrival of the 456 (he didn't like their smell the closer to Earth they got). He also gave Gwen a stunning pronouncement: she was three weeks pregnant. In shock, she left. Later, after being discovered by the British government, he was targeted for assassination. When agents arrived at the hospital to terminate him, he used his precognitive knowledge to take action, attacking his interns and escaping into the night. (TW: Children of Earth: Day One)

On the second day, he was seen in a pub near London, where his smell sense of the 456 grew even stronger; the people in the pub grew suspicious of him. After the bartender determined he had stolen a wallet, she immediately called the police, who arrested him after a brief struggle. (TW: Children of Earth: Day Two) On Day Three, he was released on bail by Gwen and Andy Davidson, and was brought to their makeshift base in London belonging to Torchwood One, after their hub was destroyed by the government. To his utter horror, however, he found himself facing the demon of his nightmares - Harkness, who hadn't changed a bit in 44 years. (TW: Children of Earth: Day Three)

In revenge and anger, he shot Jack dead, but was further stunned after Jack revived himself. Gwen was able to calm Clem down, and he was able to provide some assistance to the team again. Jack and Ianto Jones were able to get into Thames House to negotiate with the 456, who had arrived the previous day (they demanded 10% of Earth's children). When the 456 refused to go empty handed, it inflicted pain on Clem; the trauma caused internal bleeding to his body from his brain. Eventually, before it killed everyone inside Thames House, it "disconnected" him, effectively killing him in front of Gwen's eyes. (TW: Children of Earth: Day Four) His death was avenged by Jack Harkness who used the same signal he was killed with to kill the 456 Ambassador and drive off the aliens. (TW: Children of Earth: Day Five)