Blobs are a species that hail from an unknown planet and are presumably in alliance with the Irken Empire.
There have been several different blobs seen throughout both the series and the comics. Hinting that they come in all shapes and sizes, a few appear to be humanoid in nature like Eric the Blob, or doughy and pale who lack legs and arms such as the Blob Creature seen in "Abducted", Green and short like the Vomiting Blob from "Backseat Drivers from Beyond the Stars" or big and intimidating like the Conquer-Blob from Issue 20. Some blobs are non-sentient, as was the case with Cthulu.
Different Types of Blobs.Since Eric works as an intergalactic repairman, he installed the Vortian 'Splodey System on Vort's prisons once the Irkens conquered the planet and converted it into Irk's top millitary research prison, which implies that his race is in alliance with the Irkens. This is supported by the fact that in "The Frycook What Came from All That Space", he is Shloogorgh's Flavor Monster's best costumer, stated to be there everyday, and Sizz-Lorr ensured he was as comfortable as possible whenever he came into the restaurant. Also, the staff (except Zim) don't show him any disdain unlike all the other "inferior races" that come to eat.
Unlike most other aliens who hate the Irkens, Eric talked to Zim in a friendly way and even helped him out by giving him advice. He unwittingly became an accomplice in Zim's escape from Foodcourtia, and was only mildly surprised by the fact that an Irken fugitive had been inside his belly.
Maybe fittingly the mascot of the restaurant has some resemblance to the green Blobs that were seen around the planet, and thus is possibly that is from the same species which may have been a marketing strategy by the Irkens.Interestingly, some Blobs have decided to take part in the resistance against the Irken Empire and joined the Resisty, as was the case of an unnamed vomiting green blob, hinting that not all members of the species approve of the Irkens plans for Galactic Conquest and decided to take a stand against them.
Another member of the species seen was the Blob Creature who is very miserable since he is incarcerated by two idiotic aliens and can't escape due to his slug-like body meaning that he can hardly move. Unsurprisingly, Zim doesn't help him out when he asks for help, despite the fact that their species are presumably in an alliance.
It's possible that the Blobs were actually created by the Irkens rather than the species coming from a different planet. This is heavily implied by "The Trial", where we see a flashback of Cthulu, an "Infinite Energy-Absorbing Blob Thingy" created by Zim while he was a scientist working on Vort Research Station 9.
Similarly, in Issue 20, Zim creates the Conquer-Blob, a creature whose one purpose, driven into its every cell, is to crush humanity and conquer the Earth. While it succeeds, the Conquer-Blob eventually changes its mind about conquest. It restores human civilization and flies off into space to find other people to help, making him Zim's only experiment that benefits the universe rather than to cause destruction.
- The blobs are most likely inspired by the 1958 film The Blob.
- Green Blobs also appear on the cartoon Futurama, though in this case they are known as Venusians, giving them a known homeworld unlike Invader Zim which doesn't give them a known planet of origin.