Giant Devil (official name Armageddon) is a gigantic dogu-like robot designed by Professor Gill as his ultimate weapon. Professor Gill distributed the pieces of Giant Devil amongst his two children: Akira who has the general design and Rumi who possesses the blueprints for the controls for alignment between power levels. The robot served as the primary plot element for the second half of the Kikaider manga for both Gill Hakaider and SHADOW.
Giant Devil in its incomplete state could level an area of several kilometers. Its full powered state could release a ray that can have whatever approach it in a state of suspended animation. One stage of its power called Armageddon X that has a large amount of short range weapons that could wipe out an army of enemies. Its next stage Armageddon Y is said to be 100 times more powerful, giving its weapons a longer range and power. There is a final stage Armageddon Z that is said to have unimaginable power, but its capabilities have not been seen.
The plans for Giant Devil were sought out by Gill in his new form Hakaider and SHADOW in their quests for world domination. SHADOW managed to kidnap Akira and had completed the body for Giant Devil. Hakaider managed to get both Akira and Rumi in his custody to complete Giant Devil where he used it to take control of the Kikaider Brothers and Bijinder as well as wipe out SHADOW's forces. However, Kikaider was not affected by the controls and destroyed the controls for Giant Devil and later the whole robot, ending its threat for good.