In the Babylon 5 universe, a small tentacled creature that attaches itself to its victim's neck, permanently. It then burrows down into the spinal column, gaining control over its host that grows with time. The Drakh used these to control the Centauri Regent, and later Londo Mollari when he became Emperor. The only way to gain a few moments of freedom is by putting them to sleep with alcohol, but a Keeper's tolerance to it grows with time.