The Highbreed believe that their DNA is the purest of all alien species which in theoretically is seeing as they have maintained their blood purity for so long it has result in much inbreeding and eventally sterility in the entire race, or at least until Ben merges their DNA with other species allowing for genetic diversity and therefore fertility, and seek to clense the galaxy of lower life forms until they become part "lower lifeform". They've traveled to Earth to exterminate mankind. Notable Highbreeds are, the Highbreed Commander and the Highbreed Leader. The Highbreed Commander that usually fights Ben, insults him by calling Ben "scum" or even "filth". Also, during a fight with Ben, Ben actually bit the Highbreed Commander causing him to insult Ben by saying that he had infected him proving that they do think their DNA is the purest of all alien race. In the episode "Max Out", he attacks Max Tennyson, only to die when Max destroys the focus of the Null Void Projector and using it as a hand grenade. Their sizes come close to the sizes of Myaxx and Vilgax or roughly 12 ft. using the knowledge ofthe average adult's height being 6 ft. as well as that Max was roughly half the size of the Commander in "Max Out" , they are also equal in size (but superior in strength) to a 12ft. "small" form of Humongousaur. They make DNAliens do all their dirty work. It is revealed in Plumber's Helper's not all DNAliens work for the Highbreed this is only because one of them is a Plumber's Kid, though it is likely that he was actually a regular DNAlien as it is logical to assume that Helen,Manny and Pierce didn't solely capture Plumber Kid's under the impression of them being DNAlens as they had to have discover the rough outline of the DNAlien plan form somewhere as it is unlikely that with their forms they would be completely discriminate against things that look like monsters and they would need a reason to assume DNAliens are evil

Highbreed's First Appearance
Ben 10 Returns Part 1

Highbreed's Last Appearance
Ongoing