Grey Matter

Grey Matter is a Galvan from the planet Galvan Prime.

Appearance
Grey Matter is a gray-skinned, frog-like, bipedal alien only six inches tall with large green eyes. The Omnitrix symbol is located on his back.

Abilities
Grey Matter's size belies his great calculative and technical intellect and when it comes to intellect he's second to none. He can create almost anything from spare parts and deduce the function of any device at a glance. Also, Grey Matter's intellect serves as a problem solver and analytical help in difficult situations. Grey Matter's diminutive size allows him to squeeze into small spaces, and he can climb walls thanks to tiny suction cups on his skin. He also has sharp teeth, and his slimy skin makes him difficult to grab. Every time Ben chooses another alien when the Omnitrix chooses another it's usually Grey Matter.

Weaknesses
Unfortunately, Grey Matter's size makes him unsuitable for battle, and hence Ben must outsmart his enemies while using the form. Grey Matter has, however, proved very valuable when used, as he is capable of hiding in very tightly compacted areas, and the form's supreme intellect has helped in many situations.

History
Ben first transformed into Grey Matter in Washington B.C. when he saw that a gold Sumo Slammer card could be found in a box of cereal. Gwen found him looking for the card in the cereal boxes at the supermarket. Although Ben rarely intentionally selects Grey Matter, he often finds himself in that form as a result of accidental transformations, such as in A Small Problem. Most of these situations occur when Ben intends on transforming into a large, powerful alien, making his change into Grey Matter all the more ironic. It seems that Grey Matter is the one with the most accidental transformations. As Azmuth was the one who made the Omnitrix it is possible it is his DNA that is in the watch.

In the Ben 10: Alien Force two-part series finale, after completing the Ultimatrix, to his disappointment Albedo discovers that Grey Matter (as Albedo wishes to return to his Galvan form) isn't among his available list of alien forms and realizes the Ultimatrix is still synced with Ben's Omnitrix, forcing him to work with Vilgax in order to obtain the Omnitrix from Ben, only to have Vilgax double-cross him and take the Omnitrix for himself, ultimately leading to the destruction of Ben's Omnitrix forcing Ben to forcing Albedo to handover the Ultimatrix, thus leaving Albedo stuck in his Negative Ben form (on a side note it is somewhat ironic that Albedo actually wants to transform into Grey Matter but couldn't, which is ironic given that in the original series, Ben would often transform into Grey Matter unintentually or completely by accident).

Race Against Time
Grey Matter appeared briefly in Ben 10: Race Against Time, where, after getting mocked by his peers in a popular hangout, Ben transformed into Grey Matter, and rearranged the circuits of the machines in the diner to create havoc.

Ultimate Alien
Dwayne McDuffie confirmed that not every alien in the opening, so it is still unknown if Grey Matter will reappear in Ben 10: Ultimate Alien as an additional alien. He now has green eye instead of yellow-green, and the symbol is now on his chest. Otherwise, and he is now lighter grey than before.

Trivia

 * In Ken 10, Ben 10,000's son, Kenny Tennyson uses Grey Matter's form to access his Omnitrix's master control by using Grey Matter's intelligence to figure out the correct combination. Neither Ben 10,000 or 10 year old Ben thought of doing this.
 * Grey Matter is the same species as the Omnitrix's creator, Azmuth. Azmuth's former assistant Albedo was also a Galvan before he created his own Omnitrix resulting in becoming trapped in the human form of Ben Tennyson (the Omnitrix's default form) and is unable to use Grey Matter's form because both his and Ben's Omnitrix are synced together (Ben didn't have access to Grey Matter's form at the time).
 * In Italian version he is called "Materia Grigia" (Grey Matter)