The blarg were a hostile, dimwitted species. They were native to the planet Orxon and spoke the language Blargian. The way blarg is spelled varied over whether it is a leap year or not, also being spelled "blaarg."
The blarg originated on Orxon, which, in the events of Ratchet & Clank, had become so overpopulated and poisonous, that they were no longer able to dwell there without the use of oxygen masks. The blarg followed Drek's rule when he suggested building a new planet, and many blarg were commissioned into Drek's Army. But after the defeat of Drek, the blarg were forced to either continue to inhabit their polluted world of Orxon, or leave to find a new planet to live on.
The blarg vary in physique. They range from diminutive to rather muscular and bulky figures. They all have a distinctive pair of glowing eyes, which are normally gold or blue in color. Many blarg soldiers and employees seem to be unintelligent, but their scientists are brilliant inventors, rivaled only by Gadgetron. It later transpired that Drek had been polluting Orxon and was planning on doing the same to the Blarg's new world (and then re-do the process, all in an attempt to earn a lot of cash). After Drek's defeat, the blarg became less hostile to the rest of the Solana Galaxy. 
By the time of A Crack in Time, the blarg seemed to have made an alliance with Nefarious, as they were mentioned as being capable of helping Nefarious with using the Great Clock, it is possible they made some kind of deal with Nefarious, similar to Lord Vorselon and the Valkyries.
The Blargian Government were the primary government of the Blarg, headed by a Chairman. They possessed a large military might.
While considered idiots by the other races in the Solana Galaxy, the blarg still proved smart enough to adapt minor quantum compression technology, build planet destroying superweapons and planet sized harvesters. Though these feats seem incredibly advanced, in the Ratchet & Clank universe such technology is considered normal and easy to make, and that is why even the "dimwitted" blarg races could accomplish them.
The word "blarg" seems to be associated with things that are generally unpleasant in the Ratchet and Clank universe:
- Upon learning the instructions for the Levitator were in Blargian, Clank was prepared to abandon its use before Ratchet attached it to him.
- Ratchet's untested Gravimetric Warp-Drive was made of Blargian scrap metal, which caused Clank to question whether using it was safe.
- The insult "you Blarg-headed frack monkey" being spouted by Ratchet's faulty speech circuitry in his Dreadzone suit.
- Emperor Tachyon comparing the smell of Kerchu with blarg dung.
- Captain Qwark saying that the Imperial fight festival was the most fun that could be had "outside a Blargian prison camp!"
- Ratchet & Clank (first appearance)
- Ratchet & Clank: Going Commando (mentioned only)
- Ratchet & Clank: Up Your Arsenal
- Ratchet: Deadlocked
- Ratchet & Clank Future: Tools of Destruction (mentioned only)
- Ratchet & Clank Future: A Crack in Time (mentioned only)
- Ratchet & Clank: All 4 One (mentioned only)
- Ratchet & Clank: Full Frontal Assault (skin only)
- Ratchet & Clank (PS4) (re-imagined Blarg)
- Ratchet & Clank (movie) (re-imagined Blarg)
- PlayStation Home (firing range only)