They often form into mercenary bands, fighting as most mercenaries do for a group that can pay the right price. Galgs are a rare sight to Humans, and the only Humans known to have come into contact with Galgs have themselves been mercenaries. It would seem that most if not all Galgs operate for the Tau Empire, although whether or not they will work for other groups is unknown. For reasons left unrevealed to mankind, Galgs have an incredible animosity towards Humans like many other sapient species, which may indicate that they either severely dislike mankind's selfish claim of the galaxy or that man perhaps had ancestors whom had done something vile in the past.
To the untrained eye by Imperials, they were described as frog-like beings though xenologist describe them actually to be more inhuman and resemble a mass of tentacles with a bulbous head. They have six tentacle limbs instead of arms or legs. Lacking heads, Galgs instead have cluster of optical appendages. Their language resembles glass harmonium when they move their limbs.
The Galgs originate from a world called Adummin in the Ultima Segmentum. They once lived in palaces called soums built deep underground and illuminated by bioluminescent spores under ceremonial mounds called vathries. According to their beliefs beneath their soums dwells a malevolent species called the maku. It is believed that when Galgs die and do not led worthy lives the maku will drag them into their realm.
Their world was an idyllic one without war or need that remained unchanged for many thousands of years. However that changed when the T'au Empire arrived. It was through them the Galgs realized that they were wasting their lives in idle pleasures and peaceful pursuits. They Galgs eagerly join the t'au in their great work to civilize a barbaric galaxy.
- Liber Xenologis