Born and raised as a human, this "pretty boy" and his pretty sister were made into cyborgs by the infamous Dr. Gero (note: He is NOT the leader of the Red Ribbon Army, FUNimation is just stupid). Juunanagou was the first type that had an everlasting battery thingy. Therefore, he can theorectically live forever, as long as he isn't smashed into pieces. He has no memories of his former life, however, he does know that he and Juuhachigou are brother and sister, apparently Gero told them as much.

Soon after being re-born as a jinzonigen, him and his sister revolted against Gero, however Gero promptly de-activated the two and went back to work.

The next time they were activated, Juunanagou and his sister immediately saw the control mechanism and played nice with Nijugou (20-Gou; Gero transplanted his brain into a jinzonigen shell). However, the two asked about the jinzonigen labled 'Juurokugou' (16-Gou). Gero told them that he was a failure and was never to be re-activated. The two still pressed on, until Juunanagou got sick of being nice and decapitated Nijugou and then stepped on his head. What a nice way of thanking your "father."

In the alternate timeline, Juunanagou and his sister killed Nijugou, the Z Senshi, and the planet. Luckily, Mirai Trunks came back from the future and did his thing and then they Z Senshi had a chance at winning.

However, it wasn't long until Cell showed up. Cell was bent on getting the perfect form, by absorbing Juunanagou and his sister. Cell eventually absorbed Juunanagou, making semi-perfect Cell.

Juunanagou is driven by Gero's programming, and only wants to break stuff, including people. He has no soft mushy side like his sister and Juurokugou. He only wants to kill... slowly and painfully. He's a ruthless bitch is what he is.

We later see him again briefly during the Majin Buu saga when Gokou is collecting energy for the Genki Dama. The next time we see him is in DBGT, where good characters go to die in a hideous and horrible fashion.

Apparently, Gero and some other weird mad scientist (Dr. Muulo? It has an 'M' and a 'U' I think...) devise a plan. They built another Juunanagou and somehow managed to get him to fuse with the Juunanagou that's on Earth. They form "Super Juunanagou." This entire saga is super gay and has no real meaning to the series. Super Juunanagou beats everyone's ass, eventually Gokou goes SSJ4 and kills him; budget!