Grey Matter is a Galvan from Galvan Prime.
Grey Matter's small size belies his great calculative and technical intellect. He can create complicated machines from spare parts, understand the function of any device at a glance, and make sophisticated repairs to complex machines (such as a warp-drive engine). Grey Matter's intellect serves as a problem solver and analytical help in difficult situations. This allows Grey Matter to think more strategically when brute force is inefficient. In fact, Grey Matter is smart enough to know how to unlock the Omnitrix's Master Control, though he has not yet done this. Grey Matter's brain capacity makes Ben smarter about things he's never even seen before, like Kraab's alien circuitry. Grey Matter can sometimes manipulate living things by stimulating certain parts of their nervous system if such beings can be controlled by external stimuli. Grey Matter's size allows him to squeeze into small spaces and can climb walls due to microscopic pads on his skin. He also has sharp teeth and his slimy skin makes him difficult to grab. Grey Matter is the weakest alien in the series so far due to his miniscule size, but he compensates with his intellect and efficient technological and calcuative skills. Grey Matter's intelligence is not limited to technology and biology, as he is smart in general. Even if he does not know something, he can learn it very quickly. Grey Matter appears to be stronger than he looks, being able to pull strong wires. Grey Matter is amphibious and has gills. Grey Matter has a long prehensile tongue, owing to his insectivore nature. As a Galvan, he also possesses a 'pre-brain' which deals with all basic bodily functions
Grey Matter's small size makes him unsuitable for physical battle, so he must outsmart his enemies in a fight. Animals like dogs and cats can be a problem, as they may see Grey Matter as a chew toy or food to them. Despite possessing immense intelligence, Grey Matter can still make miscalculations. According to himself, Grey Matter sometimes does not know what he is talking about. Grey Matter does not know everything. Being a Galvan, Grey Matter would be vulnerable to his natural predator, the Omnivoracious, if the latter's species was not extinct.
- Grey Matter first appeared in That's the Stuff, where he escaped from Vera's house and battled a Limax.￼
- In Bounty Hunters, Grey Matter defeated Sixsix, Kraab and Tetrax.
- In Introducing Kevin 11, Grey Matter fixed the Rustbucket.
- In Brief Career of Lucky Girl, Ben tried to turn into Stinkfly to catch up with Hex, but got Grey Matter and had to ride in the Rustbucket.