Who is Dragon from Where the Mountain Meets the Moon and what is their importance?

One hundred years before the main storyline of the book, Magistrate Tiger had a painting commissioned in exchange for releasing a local village from a heavy tax burden. But it turns out that the painting had been created with magic ink and the dragon that was painted came to life once its eyes were painted in. This dragon then flew away but was eventually trapped for many years by evil monkeys. When Minli meets the dragon, she names him Dragon (he had no name before) and releases him. From there on out, Dragon is unswervingly loyal to her and often waits for days while she completes small sub-quests on their way to see the Old Man of the Moon. Dragon often sacrifices for Minli, such as when he fights Green Tiger rather than letting her be hurt by it. Dragon also trusts Minli enough to allow her to go see the Old Man of the Moon alone. Dragon displays his own ingenuity at several points, such as when he acquires the String of Destiny.