Storm King's Thunder
A prank-loving young copper dragon, Vexilanthus first encountered the adventurers while they were aboard the cloud castle of Zephyros. He asked them to clear out his lair from a mopey hill giant. They agreed to do so, and in exchange Vex agreed to assist them in defending Goldenfields from the hill giant army that was approaching.
It was later revealed that Vex had been banned from Goldenfields after using his slow breath to make the townsfolk late for church, and the temple's priest not finding the prank funny. However, after he helped save the town, the priest agreed to allow him back into town and his former perch at the top of Dragon Tower.
Eventually, the adventurer's realized that Vex could have easily defeated a single hill giant on his own, and that the whole thing was an elaborate prank to both test the adventurer's mettle and get them to vouch for him so he could get his old roost in Goldenfields back.