Dr. Gero was a very higly intelligent scientist for the Red Ribbon Army. One of the top scientists in the world, even. However, when a young boy named Son Gokou almost single handedly destroyed the Red Ribbon Army, Gero's life was destroyed. He vowed for revenge.

Gero created a small robotic insect that followed Gokou for years, allowing Gero to see and learn from Gokou's every move. Everything was read by his computers which interpeted this data. Gero had excelled at creating jinzonigen (android, man made men, artifical humans, whatever... but not cyborg). Gokou had already befriended one of Gero's older jinzonigen, Hachigou (#8). Gero continued his work at perfecting his jinzonigen.

During the Freezer Saga, Gero created his new series of jinzonigen that had an everlasting energy source, these two were Juunanagou (#17) and Juuhachigou (#18). However, since these two were built from humans, they retained their sense of free will and refused to be ordered around by the man that took away their lives. Gero deactivated them and went back to using the old series with limited energy.

His next one was Juukugou (#19, duh). This one could absorb energy and add it to its own, making it stronger. However, by this time, Gero was very old and could not continue his work in his slowly dying human body. So what do you think he did? He made Nijugou (#20). Which was identical to his human form except it wasn't human. He had Juukugou transplant his brain from his human body to his new jinzonigen shell.

Soon after, not long after. Fate came into play and two jinzonigen attacked an island 9 kilometers south of the capital. The Z Senshi was ready in this timeline. Vejita easily scrapped Juukugou after Gokou had a heart attack. But Nijugiu was left unnumbered and severly overpowered. So he ran for the hills a la Juukugou. But he made it. After getting one of his hands chopped off by Piccolo, Nijugou was able to esacape to his lab to re-activate Juunanagou & Juuhachigou.

This time, the two played it smart and pretended to be nice with Nijugou because he was "the one who made me what I am." However, Juuhachigou wanted to know what the deal was with Juurokugou (#16), and why Nijukou wouldn't allow him to be re-activated. After the Z Senshi busted down the door, Juunanagou decapitated Nijugou, and then slammed his foot down on his head. Ouchies.