The Hoolox were an ape-like warrior race. They were one of the races along with the Nin, and the similarly warlike corocdile-like Sraal, were duped into beleiving that they have rightfully bought the Earth. However, that was a mistake due to the human boy, Robbie, who was then playing with it, not knowing or intending what would happen. Not convinced with the doctor's explaination, the Hoolox launched a missile attack that was powerful enough to burn the planet. (COMIC: The Day the Earth Was Sold)
The Doctor was able to enlist the help of the formally duped but peaceful Nin to prevent the attack. In response, the Hoolox joined forces with the Sraal. Despite that, the advanced technology of the Nin was no match to their combined forces. (COMIC: The King of Earth)