The Energer Z (エネルガーZ) (at first named the Iron Z) was the original concept of the Mazinger Z. During Go Nagai's time trying to create a new idea for a manga he got the idea of going around traffic. In the original drafts, the pilot would use a motorcycle and a bridge on the back of the robot to ride up to the cockpit and control the super robot. While this was a good idea, Nagai's editor suggested changing the design due to the popularity of Shotaro Ishinomori's Kamen Rider.
The Energer Z resembled the Mazinger greatly, the only difference being a different shaped head crest and heat sinks, along with the bridge on the back.
While Energer Z did not appear in the early media, the use of a motorcycle to pilot a robot was used for the Diana A. Later, the designs for the Energer Z made a comeback in several twenty-first century media starting with Mazinger Angels Z, under the original name Iron Z. The Energer Z would appear again in the Mazinger reboot anime Shin Mazinger Shogeki! Z Hen as an early version of the Mazinger Z under the control of Tetsuya Tsurugi and later Count Brocken disguised as Kenzo Kabuto. In Shin Mazinger ZERO, the Energer Z appeared again as a prototype of the Mazinger along with the red-colored Iron Z in flashbacks.