Though I haven't fleshed them out very much the X|! were a very aggressive set of Cloner-types. Started off as cheap labour for some advanced civs shittier resource extraction operations before getting into a cancerous feedback-loop in their metadata and destroying their originators. Not magic Clones but 'force grown to adulthood in 5 years' style things. They a) wanted all the life planets and b) saw all non-X|! as a threat. In addition their origin civilization was pretty high tech in a number of fields so their capabilities were a serious threat to the Orion Sector cultures.
The Sontarans basically, but the ones from the books who would drop a billion soldiers on a world at a time. Them being engineered to be unquestioning slaves also made them quite scary - they had no real mental/cultural introspection, they never asked themselves *why* they should colonize the galaxy, they just did it because they had the ethics of bacteria with spaceships.
The Sontarans basically, but the ones from the books who would drop a billion soldiers on a world at a time. Them being engineered to be unquestioning slaves also made them quite scary - they had no real mental/cultural introspection, they never asked themselves *why* they should colonize the galaxy, they just did it because they had the ethics of bacteria with spaceships.