Robber is the Rock Breaker tribe, a mining tribe that lives underground in the Grey Eyries. Most males from his tribe toil in the tunnels until they die from fumes or a ceiling collapse, a fate the young Robber decided to avoid.
He claimed one of the three seats at the War College made available to his tribe, which put him in direct competition with another four dozen males. His lineage as a the grandson of a Matron's third daughter saw him automatically in the top ten candidates, but he had to take measures to ensure he'd get a seat. He killed another boy in an honour duel and pushed another down a mineshaft before retaliation came in the form of a snake in his bedding. He survived and replied by throwing a sack full of badgers in the alcove where the candidate who'd tried to kill him lived, disqualifying him through the mess it made. The approval he got from the matron-attendants at his viciousness disgusted him, and so he tried another angle. He talked the other remaining candidates into playing knuckle bones, and cheated well enough he claimed the third seat. This displeased the matron-attendants, who had wanted to thin the weakness out of the tribe by the killings. His alternative way to settle the matter was seen as rebellion and he was brought forward nine and nine matron-attendants, the highers and the lessers. The Matron herself took one look at him and claimed he had "seen the wind". She announced he now belonged to the Tower and could go die in a gutter for the Empress. He was seven years old when he left for the War College.
After joining, he was assigned to Rat Company as a sapper and at some point became a close friend of Hakram. When the Fifteenth Legion was formed, most of Rat company, including Robber, were given positions in it.
Robber is fairly unremarkable in terms of physical appearance. However, he is noted as having a particularly malicious look in his eye, especially when excited, and for managing to look sinister and up to no good no matter what he is doing. Catherine describes him as being able to skulk through the middle of a wide street in broad daylight.
Robber is extremely reckless, vicious, and underhanded even by goblin standards. He enjoys the general craziness of working under Catherine, and has a great fondness for theatrics, especially when used to terrify others. His personality is described as being the goblin equivalent of acting macho, which focuses less on strength and more on underhandedness and bravado than the human concept. To what degree this is his natural personality and to what degree this is showing off to impress Pickler is unknown.
Robber greatly enjoys working with Catherine, since she so frequently thinks of what he considers entertaining ways to make use of his skills. He has a more or less friendly relationship with almost everyone else from the original Rat Company.
He is also infatuated with Senior Sapper Pickler, and has something of a personal feud with Nauk as a result. He may act more extremely in an effort to impress her, although his natural personality may just be that way.
Sacrificed his life to bring down a Crab with goblinfire in Hainut. 
Robber has been called Catherine's 'Lesser Lesser Footrest' ever since First Liesse. He was later promoted to 'Lesser Footrest' after he killed Akua's father in the Doom of Liesse.
Right before his death, Robber was officially raised to the title of noble, under the aforementioned honour: Lord of the House of Lesser Footrest, to be held in perpetuity, by Catherine.