Ceph

"That's right, the owners are back! And not much liking what they found festering behind the fridge..."

- Jack Hargreave

The Ceph are a technologically advanced race.

Physiology
Cephs are cephalopod-like in form (hence their name), with three tentacles protruding from their back (though only in the Human-derived strain. The pure Ceph have five coming from their torso). They also have many red eyes.

The original Ceph have a less squid-like appearance, with actual arms (where as the human strain rely on mechanical ones) and can only survive in sub-zero temperatures. Pure strain Ceph are about 2 metres long and blue/purple in colour.

Human strain Ceph vary in height depending on function, but are all pink in colour or red if they are commanders;
 * Stalker - about 5.6 tall
 * Grunt - over 6 feet tall
 * Commander - over 6 feet tall
 * Ceph Heavy - 12 feet or taller

History
The Ceph were first encountered at the Tunguska Event by Jack Hargreave and Carl Ernst Rach. This encounter apparently lead to the infamous explosion there, and it also lead to the two men taking Ceph technology.

The Ceph apparently had colonized Earth long before the evolution of humans. A later encounter with the Ceph was in North Korea on the Ling Shan islands in the year 2020. This encounter is regarded by military types eg Colonel Barclay, as a "mess" as many lives were lost until the Ceph were eventualy nuked.

In the year 2024AD, an ancient area denial bio-weapon of Ceph origin began infecting the populace of Manhattan, New York. The humans, regarding it as nothing more than a virus, treated it with antibiotics (note that antibiotics do not work against viruses, possible plot oversight), but this merely slowed down the cellular breakdown in the infected. It transpired that the virus melted those it infected down into a kind of base tissue in order to build combat forms such as the stalkers.

Technology
The Ceph are highly advanced as their machines and structures can survive for millions of years and still function correctly. Having colonised Earth countless eons ago it is accurate to assume they are a spacefaring species.

Their weaponry seems to revolve around ice, although they do use sonic and energy weaponry along with energy shields as well. Also the Ceph apparently have the ablity to manipulate weather patterns and cause seismic anomalies; one instance of this was shortly before the attack on New York, as an increase in these anomalies was reported (this could also be a bi-product of the ancient Ceph structures waking up).

The Ceph also have many vehicles to aid them in their conquest of other worlds:

Pinger
A walking tripod weapons platform with heavy armor; its complement includes a sonic pulse, energy cannon, and some kind of energy mortar.

Ceph Gunship
This vehicle fills the role of local ground support for all infantry; it has energy weaponry as well as missile launchers.

Ceph Dropship
The dropship has no offensive capabilities of its own but acts as a troop transport.

Artillery 

The Ceph utilize some kind of mortar for bombarding enemy strongholds.