The Interstellar Revenue Decimation Service is the tax collection branch of the Imperial Galactic Government and the Federation League of Planets, headquartered in a space station known as the Corrupticon. It boasts the fastest spaceships in the galaxy, a battle fleet second to none, and the leanest, meanest group of combat auditors you'd never hope to meet.
In theory, anything in the Milky Way galaxy that moves is subject to their taxation, and anything that doesn't move will be slapped with an immobility tax. In practice this is far too difficult to enforce, and so only those who draw undue attention to themselves are targeted. Once you've been targeted, there's nothing you can do to prevent them from discovering how much you've earned, when you earned it, and why you haven't paid anything on it for six years. Their preferred method of dealing with delinquent taxpayers is to hunt them down, torture them, sell their internal organs, kill them, and then take everything owned by all their friends and family for fifteen generations.
Both the information files and monetary resources of the I.R.D.S. are so vast that at one time they had to be stored in Dimension 238 through a device called the Transatron. The inhabitants of this dimension were not pleased by all the paper floating around and used the shattered Transatron to cross into Dimension Q, directly onto the Corrupticon, which they destroyed along with everyone on board.
Besides an infamous robot named Klepto, the I.R.D.S. employs a large number of Vogons and Cyclopians but also representatives of others species who somehow manage to be equally unpleasant. Tax collectors have been known to tax each other in their spare time, spend long evenings comparing particularly stringent tax demands, and play with their tractor beam just for laughs. Whey they reach retirement age, their memories are wiped and they are sent to live as monks on planet Haven, near the Corrupticon. They cannot be released into the galactic community knowing the secrets of the I.R.D.S.