The apes serve mainly as goons and a threat to all Humans, particularly Timmy, who was trying to find a way to change things back to normal before he was captured by the apes.
They wear segmented armor reminiscent of what the Romans wore, with red pieces of cloth between the joints.
In "Abra-Catastrophe!", Bippy got a hold of the magic muffin, and made the wish to make Apes the dominant species on Earth. When the Apes were briefly the dominated species, Humans had to live like they were caveman and were considered slaves. The apes would also torture and experiment on those who would dare defy them, as was the case with Mr. Crocker and Francis. Eventually Timmy was able to change things back to the way they were, and the apes were never seen/ or heard again, after that.
The apes appeared once again in Vicky Gets Fired!, this time acting as Vicky's army when she attempted to take over the world. Factions of ape soldiers were shipped to her in giant wooden crates from an unknown source, which was usually contacted by her secretary, Betsy, whose appearance is also never revealed in the episode.