The Serial G were a type of artificial soldiers, specifically created to be insane killers.
Power and Abilities
The Serial G were vaguely humanoid, but with a more unnatural physique. Their torso were three foot long tubes, with a sphere for a head. Inside of eyes, they had phasic weapons. Their arms and legs were extendible, allowing them to be over ten feet tall. Their hands were large and made of hooks. The chassis was of a vitalium/terybdonum alloy, making them bullet-proof.
The Serial G were able to jam communication system around them. They could share their thoughts with other people. When one landed in the garden of Davey Morgan, it communicated with him (even though it couldn't speak). sharing memories, causing Davey to have nightmares of the Serial G's past. (PROSE: Border Princes)
History
Around the 16th century, the Melkenes were at war with an unknown species and losing badly. Though they had robot soldiers, they were too predictable. The Melkene created the Serial G, with no inhibitions, no compassion and no morals, effectively psychotic killers. Though they won the war, the cost was so great that the galactic community classed it as a war crime. When the Serial G were recalled, they instead wiped out the Melkene. The Serial G were held responsible for their crimes, at which point they dispersed into the Galaxy.
One Serial G came to Cardiff in 2007 and arrived in Davey Morgan's garden. As Davey was a veteran, they felt a certain connection to each other, frequently having "conversation" with each other. When the Serial G killed several teenagers who were threatening Davey, he was forced to call in Torchwood Three. Owen's attempt to fight it provoked the Serial G, causing it to attack the team. When it went after James Mayer, Mr Dine detected this and protected him, destroying the Serial G. (PROSE: Border Princes)