This writeup pertains only to the Orz as they appear in Star Control 2. Star Control 3, which they also appear in, is not covered for a variety of reasons, not the least of which are that Star Control 3 wasn't very good and destroyed a lot of mystique and mythos of the previous game.
Appearance: The Orz appear as vaguely spherical creatures with a face taking up one entire side of the spheroid. The face consists of two eyes and a strangely avian beak in normal anthropormorphic configuration with gills breathing the ethanol solution they're in mounted on either side of the face. They are light green and have two tendril-like appendages which they use for manipulation.
Since the Orz species refers to itself occasionally in the singular, and descriptions by the Arliou indicate that it is, in fact, pan-dimensional, it is possible that the Orz is just organism of more than three dimensions which appears as a bunch of different projections to us, hence the improbable three-dimensional biological configuration.
History: The Orz, if you inquire too closely into their history, will attack, so not too much is known. This is further complicated by the fact that your ship's onboard translation software has extreme difficulty in translating the Orz language, causing such statements as this:
I am *expanding!* It is so much *squishy* to *smell* you!
*Campers* are the best! I have *anticipation* and then what?
Better parties in *the middle* for sure.
The asterisked words represent inaccurate translations. In any event, the Orz certainly suddenly appeared in this sector of space without any warning, coming from a place they call *below*.
The Ariloulaleelay (better known simply as the Arliou) strongly hint that there are inter-dimensional beings which for some reason the Arilou have been protecting the humans against, and perhaps the Orz are one of them. This is backed up by the fact that during your exploration of the destroyed Androsynth worlds in Orz space your explorers find constant references specters and ghosts haunting their labs during their research with Interdimensional Fatigue Phenomena, which apparently eventually destroyed Androsynth civilization.
The Orz have some connection with the Taalo, but the exact nature of this connection, or even if the Taalo still exist, is completely unknown.
The Orz Nemesis: The Orz ship is called the Orz Nemesis. It is equipped with a howitzer turret which can be rotated around. It can also deploy space marines to invade enemy ships and kill the crew. The Nemesis is probably one of the best ships in the game: it is fairly fast and maneuverable and has a ton of firepower. While piloting it, it is best to keep your distance while strategically deploying space marines for maximum effectiveness. It will lose in close combat with ships which can easily kill the space marines.