Rou Kaioushin is an old Kaioushin who spent centuries trapped inside the Z sword, pinned to the ground by what he describes as an "incredibly strong evil fellow." When Gohan accidentally shatters the sword while training, Rou finally gets loose. He's got the same basic look as the East Kaioushin—just way older, wrinkled, with a small mustache to match.
He agrees to help Gohan unlock his potential and take down Majin Buu, but he's got a price: he wants to date an Earth woman. Seems reasonable for a guy who's been stuck for literal centuries.
There's a sad backstory here. Ages ago, Rou was apparently quite the looker by his own admission. Then some witch showed up, stole one of his Potara earrings, and slapped it on herself. That fused them permanently—he lost his good looks but gained serious magical power in the trade-off. Not exactly the deal he would've chosen.
During the Majin Buu conflict, Rou sacrifices himself so Goku can live, passing along his Potara earrings so Goku and Gohan can fuse back on Earth. Since he was already dead and in the afterlife anyway, the sacrifice doesn't really cost him much beyond getting a halo. It's more symbolic than anything.
Later, in the Baby Saga of Dragon Ball GT, he helps Goku get stronger by assisting in regrowing his tail—a process that's apparently excruciating and involves giant pliers.
Content compiled by AnimeList.moe from publicly available sources.
