Porunga Character Facts

Porunga is the eternal dragon of Namek, summoned when all the Namekian Dragon Balls are gathered. Also, since a year on Namek is only 130 days (as opposed to a year more than twice as long as that on Earth), the Namekian Dragon Balls can be gathered more often than the ones on Earth, and thus, Porunga can be called on more often than the dragon of Earth Shenron can. 
As far as physical characteristics go, Porunga is much more brutal-looking than Shenron, with a heavily muscled upper body (large pectoral muscles, shoulders, arms, and a well defined four pack). Instead of looking snake-like in appearance, like Shenron does, Porunga appears to be more alligator-like, bearing great resemblance to the Naga, a group of serpent deities in Hindu and Buddhist mythology. He has a long green slithery tail instead of legs. He also has a large fin down the center of his back, and large spikes on his shoulders and head, as well as two antennae on his forehead similar to the Namekian people. 
Like Shenron, Porunga is good and kind-hearted but being that he is a dragon, he has a temper and sometimes comes off as impatient (rather than threatening the summoner, he simply states that if the person cannot think of a wish he should "wish for nothing three times so I can go"). However, he is more friendly and patient than Shenron, and has demonstrated a greater eagerness to grant wishes; he restores Krillin's clothes as good as new as a special service, and he is even shown to be happy for everyone after Tien Shinhan and Chiaotzu are brought back to life. In the anime, he saves Yamcha, Tien Shinhan and Chiaotzu the trouble of having to traverse the Snake Way again and returns them directly to Earth when they are wished back to life. He also shows embarrassment, when Bulma says he is "kinda cute". 
Besides being more friendly than Shenron and being able to be summoned more often, Porunga is also stronger than Shenron in that he can grant three wishes instead of one or two (technically, in the Buu Saga, Shenron was capable of giving three wishes, but the attempt at reviving a mass amount of people that were killed by Majin Vegeta drained his energy to the extent that he was only capable of granting one more wish). 
Like Shenron, Porunga's wish-granting powers are limited by the power of his creator; Guru originally, and Moori later on. Any wish that is encompassed within his creator's power is able to be granted. Initially, Porunga had ability to bring only one person back to life at a time (though he could bring people back multiple times), as compared to Shenron who can bring back an unspecified number of people but can only do so once.