In the world of Dragon Ball there is a hierarchy of Gods that exist. The God of all Gods is Grand Kaioshin(Dai Kaioshin), he is the highest rank of all living things and all other Gods. Unfortunately, he was absorbed by Majin Buu when he was under the control of Bibidi. These Gods are from a race called Kaios. Kaios have special abilities and are to keep peace in the universe. Under Grand Kaioshin are four other Kaioshins, one for each sector of the universe: north, south, east and west. Under those 4 Kaioshins are 4 more Kai, one for each galaxy in a sector of the universe: north, south, east and west. Supreme Kai is the God of four galaxies in the east sector. Below is a chart which can help show you how the hierarchy for the Kaios is:

Although the main Gods are Kaios, there are minor sub-Gods who are in charge of certain taks and can be from any race. These sub-Gods don't quite fit into the hierarchy chart, so a brief explanation on each of them is shown below:

Kami:

The guardian of the Earth and creator of the first set of Dragon Balls. Kami traveled to Earth after being sent away from Planet Namek by his father. Kami competes against Garlic Sr. and takes over the throne of the God of Earth. He lives with his companion Mr. Popo in Sky Place and eventually merges with Piccolo in order to fight Cell.

Dende:

Takes over the role of Guardian of the Earth after he is brought back to the Earth by Goku from the new Planet Namek. Dende, creates a new set of Dragon Balls after Kami and Piccolo merge.

Mr. Popo:

The companion of Kami, he is the overseer of Sky Place and is very knowledgeable in the happenings of the Earth. He collects the Dragon Balls and uses them to revive the people of Namek that were killed by Frieza.

Korin:

Mystical cat that occupies the tower on which Sky Palace/Kami’s Lookout sits. He is the grower of the energy restoring senzu beans and gives good advice to Goku and the other Z fighters.

King Yemma:

The demon ogre of the afterlife and king of all Ogres. He sits at the entrance desk of the 'Next Dimension' and admits people into Hell or Heaven when they die. Certain people who did good while they were alive get special privileges and get to keep their bodies after death.

Bubbles:

Although not a god, he is the pet of one. He is owned by King Kai and plays a role in training of Goku when he arrives on King Kai’s planet. The first task of Goku’s trainning is to catch Bubbles, which he does.

Gregory:

Also associated with King Kai, Gregory also lives on his small planet and helps to train Goku. He is extremely fast and Goku must hit him with a mallet to advance in his trainning.