Monstrous Machines: Ultivac and Angrak

Ultivac was a creation of Felex Hesse and Floyd Barker, criminal scientists at first pursued by and then controlling their invincible robot warrior. It and they were defeated by the Challengers of the Unknown yet returned as a pawn of Mister Poseidon to aid the Forgotten Villains against Earth-One's Superman and the Forgotten Heroes. Despite its dominance physically and militaristically, its Achilles heal was its arrogance and ignorance.

And that ignorance was matched and, in fact, exceeded by Angrak. A gigantic mechanical pawn of the core people of the Moon and its king Gorral, the creature was feared by all. Gorral enlisted its assistance to defeat Earth-Two's Green Lantern, however its Achilles heal was its mindlessness and its relative ease at accepting suggestions including  a though implanted by the emerald gladiator to cause it to self-destruct.