Myrmidon

Myrmidons are Forerunners, presumably of the Builder rate. Several myrmidons under the command of Splendid Dust of Ancient Suns guarded the Halo installations during the events of Halo: Cryptum. It is also possible that these myrmidons comprised the Builder security units under the command of Master Builder.

Trivia

 * In the real world, the Myrmidons were a legendary nation of Greek peoples during the Greek Dark Ages, the most notable of whom was the hero, Achilles.
 * This seems to create a trend in the nomenclature of Forerunner military units, as the Prometheans are also named after a legendary figure in Greek mythology, the Titan of craftsmanship.