Halo: the Covenant
The Covenant are a highly religious hiearchy of different alien species that have technology light-years ahead of any other races. The Covenant will follow any wish of their prophets - the equivalent of our government - with zeal. Different ranks are signified by different colored armors (i.e. gold armor signifies battle commander).
"Your destruction is the will of the Gods...and we are their instrument." -Covenant Fleet Commander to USNC frigate, some 30 years before the events in Halo: Combat Evolved.
The Covenant grunt is the cannon fodder of the Covenant race and generally viewed as diminutive. Grunts serve as the ideal soldier as they throw themselves at their opponents and as they are cut down the enemy has run out of ammo, leaving themselves wide open for the higher-up jackals and elites to finish them off. Grunts can use almost any handheld weapon in the Covenant armory. Special-ops grunts have been seen carrying the fearsome fuel-rod gun.
The grunts' homeworlds contain swamps, naturally occuring pillars of fire, and the atmosphere is almost pure methane. They carry personal atmosphere tanks to survive on other planets and sleep in large sealed quarters periodically injected with methane.
The Covenant elite is the core of the army. They tend to be blood-thirsty and have a way of killing off their subordinates with hasty decisions. A noticable feature of the elite is it's hunched figure. When an elite is not wearing armor and is standing up straight the neck appears two to three times longer and the skin is mottled and gray.
The jackal is a bird-like alien. They are infamously known to carry energy shields almost impervious to human rounds. When unshielded however they prove not a problem.
The Covenant hunter is the most feared element of the army. They stand over seven feet tall in full armor and don vehicle-class armor. They travel in pairs - bond brothers - and become almost insane when their partner falls. Their most common weapon is a fuel-rod gun built into the armor around their right hand. Their entire left arm is covered by a nearly inpenetrable shield.
Engineers are a non-combat race that specialize in technical construction and repair. They gain and retain information on any piece of technology they discover over the Covenant's travels. The engineers look peculiar because they float on gas-bladders and have tenticles used to disassemble, reassemble or grab things.