From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Ogres (鬼, Oni; FUNimation "Ogre") are a race most likely from the Next World.
Great King Yama was the head of all Ogres. He also decided which souls go to Heaven or Hell. Ogres did not lie because Yama severely punished those who did ("...tongues pulled put..." in the original Japanese dub or "...will be very unhappy..." in the FUNimation dub). In the Japanese dub, Ogres often spoke in strange ways, adding unnecessary signature sounds at the end of each sentence.
Ogre leading and guiding souls
The first one who was shown in the anime was a blue guy in white shirt and a tie who guided the line of dead souls with a megaphone. This would be a recurring image in the Next World, though the exact appearance of the Ogre can be different every time. Most Ogre were blue, had black hair and one horn, and dressed smartly, as they wore a shirt and a tie. They appeared throughout Dragon Ball Z usually whenever their boss, Yama, was seen. They were also seen in Dragon Ball Z: Fusion Reborn, during the Super 17 Saga in Dragon Ball GT when Goku was trapped in Hell, and in the last episode of Dragon Ball GT, "Until We Meet Again..." when Goku visited Piccolo in Hell.
Great King Yama
Main article: Great King Yama
Yama was the boss of all Ogres and judged the dead. A line of souls led to his office where he decided whether a soul went to Heaven or Hell. Compared to the other Ogre, he was of a different color, had a beard, two horns, and a helmet (it was unclear whether the horns were his own or belonged to the helm), and was colossal in size. Only his mahogany desk was at least three times taller than Goku, who was able to fit in one drawer. Yama was strong enough to stay in control of any situation and could easily overpower Raditz. Later in the series, when power of the villains increased, this became less impressive. Yama later made a few cameo appearances in Dragon Ball GT, such as when he sent Piccolo to Hell during the Super 17 Saga, and appeared in Fusion Reborn when he was trapped in his office by Janemba's barrier that Pikkon slowly destroyed while Goku and Vegeta fought against the monster.
When Yama agreed to send Goku on the Serpentine Road, he provided him with a guide who took him to the start of the road. The Guide (案内人, An'naibito) Ogre seemed to be more intelligent and knowledgeable than most of the other Ogre, as he wore glasses and had two horns instead of one. His exact function in the Next World was unknown, but later he met with Uranai Baba and gave her Goku's message for Turtle Hermit (which reached him via Kami and Yajirobe). He was again seen during the Majin Buu Saga at the Check-In Station after Goku discovered that Gohan had not been killed and in the final season of Dragon Ball Z as he watched the battle against Boo with Yama.
The Guide spoke with adding はい (hai, literally meaning yes or indeed) to each sentence.
The Driver (運転手, Untenshu; Literally meaning "Driver") Ogre was first seen when Goku ran along Snake Way. He met the Untenshu driving a cleaning machine along Snake Way. The driver asks Goku if he wants to hop on the back and get a lift with him. Goku obliges and falls asleep. But, when the cleaning machine hits a bump on Snake way, Goku is thrown off the machine and off of Snake Way. The driver, doesn't notice however. He is then seen again a couple of episodes later when Goku is back on Snake Way and runs past him. The driver notes that he looks familiar, and since he is not looking at where he is going, crashes off Snakeway. The driver speaks with adding おに (oni) to each sentence.
Gozu and Mezu
Gozu and Mezu were two watchkeepers of Hell. Gozu was the second strongest Ogre after Yama, while Mezu was the second fastest Ogre after Yama. Mezu looked just like the Guide Ogre, but his skin was red and he was much more buff (but still wore glasses). They wore t-shirts with 'HELL' written on them in matching color. In the Ocean Group dub edited version, the 'HELL' label is airbrushed into reading 'HFIL', which additionally is worked into the plot of the episode as being an acronym for "Home for Infinite Losers".
Very much like the Driver Ogre, Gozu and Mezu spoke with おに (oni) in every phrase.
In Dragon Ball Z: Fusion Reborn, a teenage Ogre named Saike Demon was careless while working the Spirits Laundry Machine (distracted by his death metal music) and forgot to change its tank. The tank overflowed, and Saike Demon was surrounded by thousands of years of spiritual waste. The purplish-gray smoke mutated his body, and turned him into the demon, Janemba. At the end of the film, after Janemba was hit with Gogeta's Soul Punisher, he transformed back into the teenage Saike Demon, who then ran away frightened. Saike Demon had red skin and two horns.
Another Ogre appeared in Fusion Reborn, though he was not named. This Ogre was the only witness to Saike Demon's transformation into Janemba and rushed to tell Yama, though he was covered in crystal along the way. This Ogre had blue skin and one horn on top of his head.
Only one female Ogre appears in the series. She is an air hostess who can be seen in "Warriors of the Dead".