Procrustes was a giant and a son of Poseidon. He was a rogue smith and bandit from Attica who physically attacked people by stretching them or cutting off their legs, so as to force them to fit the size of an iron bed. In general, when something is Procrustean, different lengths or sizes or properties are fitted to an arbitrary standard.
Procrustes is a son of Poseidon with a stronghold on Mount Korydallos, on the sacred way between Athens and Eleusis. There, he had an iron bed in which he invited every passer-by to spend the night, and he killed everyone by stretching them if they were too short and chopping off the extras if they were too tall. Procrustes continued his reign of terror until he was captured by Theseus, traveling to Athens along the sacred way, who "fitted" Procrustes to his own bed.