Vex

The Vex are a partly robotic, time-traveling alien species. From their stronghold on Venus, they launch endless waves of metal armies towards human civilizations in an enigmatic quest for domination.

Biography and Morphology
When they appear in our solar system, Vex arrive by way of warp gates set up around the galaxy from an unknown location or time. A variety of reports claim that the Vex appear to be mass-produced machine units. No official relations have been made with them, as all attempts to communicate with the Vex have failed. Their bodies are made of an unknown metal alloy resembling hammered brass,  yet they are not entirely mechanical; some organic materials are present as well. Their routines and ceremonies remain mysterious and illogical to humans. They are hostile, unrelenting, and deadly. The Vex despise the Cabal as much as humanity and are constantly fighting them on Mars, keeping Cabal operations from expanding further into the system.

Bungie has described the Vex as having a "fascinating" fiction behind them, "which, in turn, creates one of the coolest deaths in the game."

Geography
Vex are known to inhabit a massive stronghold on Venus called the Citadel. While they also have a presence on Mars, other locations are unknown.

Goblin
Goblins are foot soldiers and cannon fodder that defeat their enemies by overwhelming them in huge numbers.

Hobgoblin
Hobgoblins resemble Goblins, but are larger and can be distinguished by their distinctive tails.

Minotaur
Minotaurs are even larger than Hobgoblins, with broad shoulders and three glowing eyes.

Cyclops
Cyclops are large, T-shaped, one-eyed Vex.

Hydra
Hydras resemble "robotic centipedes", and float through the air to attack from turrets attached to each segment of their wriggling bodies.

Harpy
Harpies are smaller Vex that dart in and out of battle, firing from mouths filled with filaments.

Praetorian

Factions
Currently, six factions within the Vex army exist. These include:

Descendants
The Descendants is an ancient faction located on Venus, who have been seen multiple times by survivors of the Vault of Glass. They are portrayed in white and gold with exotic attachments to their heads.

Hezen Corrective
The Hezen Corrective is a faction located on Venus, with the primary objective of seeking out and destroying the House of Winter, a faction of the Fallen army. They are portrayed in plain bronze.

Hezen Protective
The Hezen Protective is a faction located on Venus, with the primary objective of defending the Vault of Glass and the Endless Steps. They are portrayed in gold with white stripes.

Precursors
The Precursors is an ancient faction located in Venus, who have been seen in the darkest, deepest portions of the Vault of Glass. They are portrayed in black with characteristics similar to feudal China's military.

Sol Divisive
The Sol Divisive is a faction located in the Black Garden, most of whom are frozen in rapture. They are portrayed in green with moss hanging from their bodies.

Virgo Prohibition
The Virgo Prohibition is a faction located on Mars, and are prominent enemies of the Cabal in the Meridian Bay area. They are portrayed in blue and black.

Battle Tactics and Technology
For the Vex, their battles are all about overwhelming numbers and massive armies. Little else is known about their battle tactics, but players should remember that the Vex weak spot is not the head (like with most enemies and for players) but rather the center of their torso, where their glowing power core is vulnerable.

Trivia

 * The Vex are designed to resemble a "classic science-fiction machine race" mixed with the "inscrutable motives of a timeworn Lovecraftian nightmare monster." The result is not a typical science-fiction android race, but rather a "mixture of robots and creatures" that fight their enemies with "endless waves of metal armies".
 * If they take enough head damage, Vex will not die, but will contine to attack.