Shenlong, known as Shenron in the English dub, is the wish granting dragon summoned when all of Earth's Dragon Balls are gathered. Shen Long can bestow any wish as long as it does not exceed the power of his creator, who must be still alive.
Shenron was created by Kami when he arrived on Earth. He was compelled to do so as a Namekian, who created the original Dragon Balls and their eternal dragon Porunga. After Kami fused with Piccolo, Shenron was revived by Dende.
Shenlong cannot bring back a person from the dead more than once. Shen Long can originally only grant one wish, but after being revived by Dende, he is able to grant two at a time. In Dragon Ball Super, Shenron stated he has always been able to grant three wishes since Dende's alteration, but wishes that revive many and restore planets take too much power and require using two wishes.
Shenlong often threatens to kill the summoner if they do not quickly make their wish, but never follows through with it.