Ammet is a character from The Ring of Solomon.
He was a marid of the seventh level in the service of Khaba the Cruel. First meeting each other when Khaba was very young, Ammet grew to love Khaba - claiming that Khaba's goal is one with his. This puts him in disagreement with his fellow spirits.
Ammet's preferred guise is a replication of Khaba's shadow, although it is always dark and long no matter what time of day it is.
Ammet was last sighted being corked into a small wine flask by Uraziel, the great Spirit of the Ring, as ordered by Bartimaeus. Ammet was to be bound in the bottle for a several thousand years to "reflect upon his sins against fellow spirits" and especially Bartimaeus.
In Egyptian mythology, Ammet is a beast of the Underworld that would eat villains and robbers' bad hearts.