Dragons

What is a Dragonball Dragon?

A Dragonball Dragon is created when the Dragonballs that correspond with that dragon are created. The dragon then lies dormant at the center of the planet until all 7 of his Dragonballs are gathered. 

Summoning the Dragon

A Dragonball Dragon is summoned when the person that collected all 7 of his Dragonballs brings them together. Once together, the user must resite some phrase depending on what origin and language he is. For example, on Earth, a number of different variations of chants exist. They all are pretty close to the same meaning though.

"Come forth Eternal Dragon, and grant my wish!"

At this point, the Dragon is arroused from his deep slumber, and is presented before the user via the gateway that the 7 Dragonballs create.

Depending on the Dragon's mood, the user will either be rushed into his wish(es), or will be given all the time he/she needs to think of his/her wish(es).

The Power of the Dragons

The power of wish making comes from the creator of the dragon. When the dragon grants a wish, it is granted with the power of the person who created it. For example, when Shenron (Kami's dragon) grants a wish, Kami's power is used. The more powerful the creator of the dragon is, the more powerful the dragon is, and vise-versa. This is shown by comparing Shenron and Porunga (the Namek Dragon). Shenron only had the power to grant one wish. Also, Shenron could also revive a person once. On the other hand, Porunga was able to grant three wishes, and revive a person numerous times as long as the revived person died of an un-natural cause (being murdered, etc..).

The Dragons

Shenron (Earth)
Shenron is the Dragon created by Kami (the unknown Namek). This Dragon has the ability to grant one wish, and revive a person once. Shenron's power is very limited compared to the original dragon. However, after Kami revives the dragon after Piccolo Daimo destroys it, Shenron's power increases. He becomes larger in size, and his granting power increases. After Kami fuses with Piccolo, Dende recreates Shenlon once again. This Shenlong is even more powerful than the last. Dende gives the dragon two wishes instead of one. Shenlon is put to rest once fuses with Goku giving him ultimate power. 

Porunga (Namek)
Porunga is the original dragon created at the beginning of the Namek race. Porunga is known to be the most powerful (friendly) dragon of all. He has the ability to grant 3 wishes, and revive a person an infinite number of times, as long as that person died an un-natural death. If they were killed by natural causes, the person could not be revived. It is believed that there were two versions of Porunga. One Porunga before the Namek Cataclysm, and one created after. This is not confirmed in the series however. Porunga is MUCH larger than Shenron.

Comparing the two dragons next to a familiar object (Kami's lookout)