The military sector of the private corporation, the RDA (Resources Development Administration), who's responsible for all operations involving the moon of Pandora, located in the Alpha Centauri System. As such, they were the ones responsible for the destruction of the Omatikaya Clan Hometree, followed by their assault on the Tree of Souls during the Pandoran War between the humans of the RDA and the Na'vi.
Their forces are mostly made up of mercenaries and former soldiers (i.e. Jake Sully). Their vehicular arsenal includes mechas and aircraft (most notably bicopters). In the second movie, it was expanded to include exoskeletons, boats, and submarines.