Gravid Rust is the obnoxious and evil son of Ronald Rust and heir to the Rust land and title. Vetinari describes him as an "ignorant, arrogant, pompous idiot". He is first encountered as the Rust son who was arrested by Sam Vimes and brought before the Patrician for shooting a servant for allegedly setting his boots out the wrong way round. He is described by Colonel Charles Augustus Makepeace as a greasy lad with a name like a pregnant frog, which. in fact he has since 'gravid' means pregnant with eggs or young and is used to describe reptiles, fish and amphibians - reptile being the operative word in his case.
In Feet of Clay he (or his father) was the chief suspect in paying for an assassin to kill Vimes. The assassination attempt failed when the assassin was caught by Vimes' elaborate anti-personnel traps which made the Ramkin house a death-trap for unwanted intruders and found himself hanging above the dragon pens.
In Snuff, he surfaces again as Vimes adversary. He has a certain charm and uses his 'upper class' standing to persuade people who should know better to join him in his crimes. Gravid organizes the forcible removal of the goblins fon Hangman's Hill, (which is a part of Vimes' estate), and ships them off to Howondaland as slave labour for his tobacco plantation. When he ships his tobacco back to market he uses the tobacco barrels to smuggle troll drugs, included the deadly Crystal Slam, Slab, Slice, Slap, and Slunkie into Ankh-Morpork along with the tobacco. His tobacco farm keeps the goblins under such horrific living conditions that most don't so three years later he has to move a second shipment of goblins to Howondaland, To assist him he employs the ruthless killer Stratford to eliminate any witnesses and loose ends. Unfortunately for him, this time Vimes is on the scene, on vacation at his country estate and his plans are foiled.
While most of Gravid's lackeys and smugglers are caught, and the corrupt magistrates removed, Vetinari is forced to point out to the enraged Vimes that slavery of goblins was not then a crime (goblins having being classed as vermin) and Gravid could not be brought to trial for his actions. The Diamond King of Trolls however, demands that Gravid be sent to him for trial (and near certain execution) for his role in the manufacture and shipping/smuggling of lethal troll drugs. Since the Patrician knows that it would not be politically feasible to hand over the son of a prominent Ankh-Morpork aristocrat to a foreign power to kill, regardless of his crimes, he exiles him to Fourecks instead and ensures that he is disinherited by his father, losing his title and position. Vimes sees this as 'a nice holiday in the sun' , a completely inappropriate sentence for a murderer and trafficker in human and non-human misery. The reality is somewhat different than the sentence however as Drumknott mentions to Vetineri that the Morporkian Embassy in Fourecks employs a clerk named Arachne with a particular interest in venomous spiders. Vetinari as the resident tyrant has the option of operating outside of the Law without sanction, unlike Vimes who must maintain the law. It is pretty clear that Gravid will not be returning.
The exile of Gravid Rust bears a striking similarity to that of the Roundworld case of Lord Lucan who in 1974 tried to murder his estranged wife one dark night. Incredibly, he got the wrong woman, and bludgeoned his children's nanny to death, then fled in panic. The British nobility closed ranks in protecting one of their own, a less than edifying example of their sense of ingrained privilege and of being above the law. The police claimed to have tried their hardest to crack the case, but were in part deterred by a sense of social expectations - ie, you cannot haul in relatives of royalty and give them the same sort of robust questioning you wouldn't think twice about giving to an Irish bombing suspect, a person of colour or a striking miner. Comment was made that "It was only the nanny, for goodness sake!" and the British nobility made it clear (as a challenge to any authority that believed it could treat them like commoners) that they knew perfectly well where Lucan was, but were not going to tell. Lord Lucan's wife stated in an interview that she believed he committed suicide in 1974. However, it was said that in 2011, a criminal who fled justice in 1974 and was covertly helped out by cash handouts from other nobles died in exile, possibly in Australia or New Zealand.