Croup and Vandemar are an age-old pair of overly sinister assassins who seem, to a great degree at least, invulnerable. Vandemar serves as the muscle of the operation. He wears a ring made of raven skulls and is willing to eat anything.
In "Neil Gaiman's Neverwhere", Vandemar and Croup are hired by the angel Islington to murder all but one of a noble family of "openers" from London Below, and bring the sole survivor back so that she may create a door back to heaven. In the end, the two are sucked through a door to who-knows-where. It's a safe bet they survived, though.