The embodyment of the Hive. The Leviathan is a massive creature, on the scale of a large capital ship, heavily defended both by its own means and by its many minions. Created by the joining of many minor Hive drones into a single creature, when fully completed it becomes a single contiguous being and bears no likeness to the nature of its creation. Creator of the Hive Queens. (Information comes directly from the developers wiki site found here.

The Leviathan rarely stirs from its Stronghold, surrounded by large clouds of its many lesser minions, which often adopt geometric flight patterns around its vast bulk.

Court of the Leviathan

Leviathan w/ Queen

The Leviathan is always surrounded by eight Hive Queens. Whenever a Queen is dispatched to rule a new Bastion, another Queen is created to take her place in the Court. The Court sees to the maintenance of the other minions within the Stronghold, and act as destinations for those remote Collectors who have no other Queens nearer to their respective Settlements.

Minions of the Leviathan

The Stronghold is filled with literally hundreds of other minions of various types. Observers are always associated with sightings of Leviathans, worshipping in large patterns, lending further credence to their nickname of "Eyes of The Leviathan". Collectors, Assaults, Guardians and Overseers fill out the rest of the living colony.