Black Hole Planet 3 Aliens

The Black Hole Planet 3 Aliens (aka "Simians") are a race of humanoid ape like sentient beings who construct a colossal Godzilla-like robot, dubbed Mechagodzilla as a tool for world domination.

First Wave
They establish a secret base in Okinawa, only to be discovered and killed by Interpol agents, while their creation, Mechagodzilla is destroyed by the combined strength of Godzilla and King Caesar.

Second Wave
A new army of Planet 3 Aliens returned the next year in Terror of Mechagodzilla (1975) with a rebuilt Mechagdozilla, and a plan to destroy Tokyo to rebuild it as a high-tech city (and branch out from there). The second wave of Planet 3 Aliens were disfigured humans wearing rubber masks (similar to the underground mutant race depicted recently in Beneath the Planet of the Apes). This time the aliens joined forces with a vengeful scientist named Shinzo Mafune, who controlled the dinosaur Titanosaurus. The aliens didn't really care for the scientist, and merely saw Titanosaurus as a way to weaken Godzilla before he faced Mechagodzilla. After Mafune and the Planet 3 Aliens have since settled their differences, Mechagodzilla and Titanosaurus attacked Tokyo, and were faced with Godzilla. After a long, long fight, Godzilla eventually triumphed over both foes, blowing up Mechagodzilla in a giant chasm and (apparently) killing Titanosaurus (this was never really confirmed, although that particular monster hasn't been heard from since, and in the actual movie apparently fell over a cliff). The Planet 3 Aliens tried to escape in their spacecraft, but they were blown out of the sky by Godzilla. All remaining aliens were already killed by Interpol agents and the military.

Technology
The Planet 3 Aliens, like the Nebula M Aliens, didn't seem to possess any impressive technology other than their ability to construct Mechagodzilla. The Second Wave aliens, however, wore silver bulletproof suits. Also like the Nebula M Aliens (and the Kilaakians), the Planet 3 Aliens' human appearance was merely a disguise.

Trivia

 * They are a parody of the ape race from Planet of the Apes.
 * According to the German release of Mechagodzilla 1's movies, they possibly helped in the creation of Mechani-Kong.
 * They return in the Dark-Horse comics of Godzilla and the Toho Cartoons website as nonprofit on Toho Kingdom Website.