The Dragonball Dragons are a creation made to fulfill a wish of the gatherer of all its 7 Dragonballs. It is made from a figurine that the creator enchants and brings to life. After the dragon is in existence the dragon then resides in the center of the planet until the dragonballs are collected and he is summoned. When summoned the dragon appears and grants any wish or wishes, within it's power. A dragon's power cannot exceed the power of its master, therefore if the creator is weak the power and strength of the wishes that the dragon can grant are weakened. After the wish or wishes are made the dragonballs scatter and the dragon returns to his peaceful slumber beneath the planet.
Shenron is the dragon that is called forth when the Earth dragonballs are collected and the chant, "Come forth Eternal Dragon, and grant my wish!". He was created by Kami and again called forth by Dende, who used Shenron for his set of dragonballs after Kami and Piccolo fused into one again. Under Kami, Shenron was not very strong only able to grant one wish per summoning and only able to revive someone from death. But later Piccolo Daimo (Kami's Evil half) destroyed, luckily the figurine was not hurt and Kami resurrected the dragon, this time more powerful because Kami's power had increased. After the resurrection, Shenron was larger and could grant much more powerful wishes. Shenron was again killed when Kami and Piccolo fused back into their original form, this made the Current Shenron inactive but revived Kami and Piccolo's first dragon, the dragon of the Black Star Dragonballs. But Earth still needed a dragon, so Dende was brought from Namek to become the new guardian of Earth and revive Shenron. This time Shenron was enchanted with more power then ever before and was able to grant two wishes at one time and revive multiple people at a time. Shenron is last seen when he fuses with Goku at the end of Dragonball GT.
Porunga was the first dragon created and is one of the strongest dragons ever created. He is summoned after the 7 Namek dragonballs are collected and the namekian chant is said. He was created by an Unknown Namek before Planet Namek's apocalyptic years under the storms and drought. He was then revived by Guru when Guru created his set of dragonballs. Guru was the creator that named Porunga and also made him exceptionally powerful. Porunga is able to grant 3 wishes at one time and revive multiple people per wish. Porunga is only destroyed again when Guru dies on Planet Earth. Guru's predecessor, Muuri, revives Porunga to be the dragon of New Namek's dragonballs. The amount of power Muuri bestows upon Porunga is uncertain but it is thought to be stronger then that of which Guru bestowed upon him.
Red Shenron is the dragonball dragon of the Black Star Dragonballs, he is the most powerful dragon to ever be created being that he was forged from both good and evil. He is the creation of Kami and Piccolo in one body. He is so strong that he can grant any wish and that wish may never be undone. He only appears a couple times in the Dragonball GT series and makes a few powerful wishes.
Evil Shenron is the dragon of the Earth Dragonballs after the negative energy has been built up to greatly, he really has no name so he is best describe as Evil Shenron because his creator was the creator of Shenron, but Shenron was good. He is very evil and dineies the wish of his summoners. He is rather big and smokes cigars, when he is first summoned he blows smoke in the summoners faces when they request a wish. He denies them their wish and then leaves in a gust of violent wind and expel 7 Evil dragons across the planet.