Rou Dai Kaioushin is a Kaioushin who came out of the Z sword, in which he had been trapped and stuck to the ground by an old enemy, according to him a "incredibly strong evil fellow". He resembles the East Kaioushin, but with an older, wrinkled face, and a small mustache. Son Gohan releases him during the Majin Buu Saga when he breaks the Zeta sword, while trying to cut a block made of the strongest material in the universe. After being released, he agreed to help Gohan unlock his full potential so he could defeat Majin Buu, but only in exchange for getting to date an Earth woman.

Centuries ago, he used to be quite handsome by his own standards, but a hideous witch came up to him and stole one of his Potara Fusion Earrings and put it on. Ro Dai Kaioushin was instantly combined with the witch permanently. While he lost his looks, he gained more magical power. In the Majin Buu Saga he sacrifices his life so Son Goku can live, and gives him the Potara earrings to fuse with Gohan on Earth. However, as he was already residing in heaven, his death had little effect aside from producing a halo over his head.

In the Baby Saga of Dragon Ball GT, he helps Goku become much stronger by helping him regrowing his tail, a painful process involving a giant set of pliers. Source: Wikipedia