What are The Hive in Bungie's Destiny?

The Hive is an enemy species hostile to the remaining human population on Earth.

Very little is known about their origins or traits though Bungie have alluded that they have a deep mythos and back story which will hopefully be revealed in game. Bungie have nicknamed the Hive "Space Zombies".

Bungie's Chris Barret has said of the Hive "They’re the most fantasy-inspired race. We’ve imagined them as this ancient alien race that’s kept themselves alive by some magical means for millennia. They just float through the solar system on these big, sarcophagus-looking ships.

It’s really playing up the feeling of zombies and fantasy undead. It also plays with the feeling of royalty, like they might have kings or they might have knights.

Their main units are a mixture of organic and inorganic so they’re not clothed like a lot of units. You’re not sure if the armor is organic or if it’s ceremonial armor that they put on a million years ago and it’s sort of grown into their skin. An organic shell that’s sort of grown in a way that almost resembles knights’ armor. You’ll see their dry, mummy-like flesh exposed. And then when you shoot them they’ll burst into dust and embers

Given what has been revealed so far Hive appear to have some kind of supernatural abilities, including the ability to hover or float and manipulate energy and electricity

Hive have been spotted hiding out on the Earth’s Moon, dwelling with massive underground moon base which is nicknamed by the Guardians as The Hellmouth.

I'm enthralled. No really. I am. 

Classes of The Hive

There are various classes of the Hive. 2 have been made public:

Thrall

Thralls may be considered the basic class of Hive.  Brown in color and preferring melee attacks using their long fingers tipped with sharp claws. They have no visible eyes and, in some places, their skin has rotted away to expose their skeletons. Their basic armour appears infused with their bodies.

Knight

Knights may be considered a higher-ranked class of Hive an feature more lively armor-and-cloth adornment on their persons. They appear to wear helmets with optical qualities and seem to lack the long fingers and sharper claws of the Thrall class. They have been spotted wielding energy- or plasma-based weapons.

Barret also said "Imagine when you look at pictures of shipwrecks underwater and they’re just kind of covered with barnacles and they look like they’ve eroded because they’ve been there for a long time. We want to make their ships feel like that. Basically spaceships that feel like they’ve been covered in space barnacles or whatever and have been eroded because they’ve been moving like shipwrecks for millennia.

It’s much more darker, gothic inspired. But still alien and sci-fi at the same time. We’re trying to mix those two, but they’ll have what might typically feel like a dungeon or more ceremonial throne room-like spaces or dark corridors filled with webbing."

Here's an Ogre which will only be brought down by the most skilled Guardian Fireteams...

Here's another Thrall