From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Onio (オニオ, Onio) is a comic character poking fun at the previous image of Saiyans as cool, good-looking people. Onio lands on Planet Earth for his honeymoon and decides to kill the Human race in order to make Earth his summer home. He bears much resemblance to Suppaman from one of Toriyama's previous manga, Dr. Slump. When Neko Majin Z touches his wife's breasts, Onio is enraged and becomes a Super Saiyan. He then quickly loses in the fight. Like all Saiyans, his name is based off of a vegetable, in this case the "Onion".
Onio made his first appearance with his wife Honey in Neko Majin Z when he came to Earth looking to making the planet his summer home. Neko Majin Z thought that they were tourists and goes to them dressed up as a Koala. Neko Majin Z's friend (a boy with no name) asked them if they wanted a photo so they could show off. When the boy took the photo, Neko Majin Z casually fondled Honey's giant breasts. This made Onio really angry and he transformed into a Super Saiyan. Onio then kicked Neko Majin Z away, but Neko Majin Z came back and a battle began. Neko Majin Z also became a Super Saiyan and made quick work of Onio. Honey then dragged Onio back into their spaceship and they flew away.
The next appearance of Onio was in Neko Majin Z 2 when he came to Earth with Kuriza for revenge. When Onio arrived, he found Neko Majin Z about to start a match against Thunderbolt. Onio's interruption caused Neko Majin Z to become mad and he ended up kicking Kuriza into the ground, even finding oil this way. After Kuriza transformed, he gave up and Onio and Kuriza stayed with Neko Majin Z until they could fight again (they never fought again...).
He also appeared in Neko Majin Z 3 where he was playing soccer with Kuriza, Neko Majin Z, and the boy with no name. The manga began with them playing soccer. Onio passed the ball to Kuriza, who then kicked it up into the sky. When Neko Majin Z and Onio went to get it and Neko Majin Z hit the ball, they saw an Attack Ball. The Attack Ball belonged to Vegeta, who had been sent to look for Kuriza and Onio by Freeza's orders. Onio said that they were on Earth because there was one outrageously strong guy, Neko Majin Z. Vegeta began to fight Neko Majin Z, but soon lost and had to turn into a Super Saiyan. Onio informed Vegeta that when he had tried to fight Neko Majin Z, he also had become a Super Saiyan with no effect against Neko Majin Z. Vegeta suddenly acted like he had a phone call and left. Kuriza asked if a cellphone signal could reach a planet like Earth to which Onio answered that it was out of range.