Mechani-Kong was both designed and built by the international criminal, Dr. Hu, to mine the radioactive Element X from the Arctic underground, but the robotic ape failed his creator, the radiation of Element X damaging his controls. However, Dr. Hu came up with another plan to abduct the real King Kong and using Mechani-Kong, hypnotize Kong to mine Element X instead. However, the combination of Kong’s mind and the cries of Nurse Susan Watson, who Kong had a liking for, were able to overcome the hypnotism and Kong escaped to Tokyo, with both Mechani-Kong and Dr. Hu in hot pursuit.
In Tokyo, King Kong and Mechani-Kong battled up the side of Tokyo Tower, both monsters getting their shots in on one another. In the end, an attack back on Dr. Hu's ship crippled Mechani-Kong's controls and turned the tide of battle in Kong's favor. The crippled Mechani-Kong then fell from the tower, crashing into the street below and shattering into several pieces.