Dragons

Shenlong:
Shenlong is the Dragon of the Earth Dragonballs. He was created by Kami when he came to Earth during Nameks global warming. At the beginning of Dragonball, you could go see a Shenlong and just get your wish, but Kami decided that only the people worthy could get a wish, so if someone wanted a wish, they would have to collect the Dragonballs. The Dragonballs were scattered all over the globe. This made it very hard for people to collect the Dragonballs, so Bulma created a device that would find them called a Dragon Radar. Shenlong can only grant one wish and can't grant the same wish twice. Shenlong was summoned whenever someone said "Idee Yo Doragon" or in English "Come out Dragon". When the Dragon is summoned, the sky turns black and the dragonballs start to glow and the light shoots up and the Dragon appears. When the Dragon appears, he will grant the first wish, no matter who says it. Shenlong can only grant a wish that doesn't exceed the power of the creator. Also Shenlong will die if the creator dies. So if Piccolo or Kami die, the Dragon dies as well. At the end of the Android Saga, Piccolo fuses with Kami(a Namek fuse) so a new God for earth is needed. Dende becomes the new God. After a little bit, Dende upgrades the Dragon so he can grant Two wishes.
Porunga
Porunga is the Dragon of the Namek Dragonballs. Porunga was created by Saichouro. After Saichouro died, the job of dragon keeper was given to Muri(Guru). Porunga is a lot bigger than Shenlong. Porunga's first appearance was in the Namek Saga when Gohan, Krillin and Dende summoned the Dragon to bring back Piccolo, Yamcha, Tien and Chao-Zu. Here they learn that Porunga is different from Shenlong, because Porunga can only bring one person back at a time. For the Namek Dragonballs, you need a password to awaken the Dragon. The password is "Takkarato Popporunga Pupirittoparo" which is in Namek. Porunga can grant three wishes and can grant the same wish more than once. At the end of the Buu Saga, Porunga was given a power up to grant more than one wish.