Eudemon

Eudemon, officially known to the UNSC as "X49-05", is a satellite orbiting an unknown planet and a Unified Earth Government colony world. It was discovered by a pioneer group after the Human-Covenant War. A simulation of a cave found in the moon was later used by the 's SPARTAN-IV complement for training.

Trivia
A Eudemon is a kind spirit/demon in Greek mythology.

List of appearances

 * Halo 4