Wisp was the dragon who guarded the Nunchucks of Lightning, one of the Four Golden Weapons, before merging with its fellow guardians to become the Ultra Dragon.
WIsp was charged by Master Wu with protecting the Shurikens of Ice, and thus dwelt at the Frozen Wastelands. He was later awakened in "King of Shadows" when the Ninja obtained the Nunchucks, but they were able to escape him. However, in "Weapons of Destiny" Kai succeeds in befriending Flame, and his fellow Ninja follow his example to tame Rocky, Shard, and Wisp. Using the dragons' power to travel between worlds, the Ninja then make their way into the Underworld to rescue Wu.
In "Day of the Great Devourer", it is revealed that Shard has merged with the other three dragons and become the Ultra Dragon.