As yes, the quasi-intelligent orangutans with an instinctive knowledge of complex technology are called 'Jokaero'. Along with Petra Squirrels and Grox they are still hinted at in a lot of 40k books even today although no rules for using them in games have appeared since the days of RT.
^
As you'd expect the few miniatures GW produced to represent them are rather fought after.
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~The ravings of a single mad Goblin is bad enough, but such a power-hungry, malice-filled creature as Mortis can never hope to be understood~