The Hudson River Dragon is the dragon that resides in the tunnels of the Hudson River in New York.
Living in New York
The Hudson River Dragon took residence in the Hudon River in New York, where she began collecting a variety of items for her hoard. Free Trader Beowulf listed her as a potential source to interview to talk about how to contact the gods. 
Quentin Coldwater and Julia Wicker traveled to the Hudson River Dragon's nest in New York City to retrieve Wicker's Shade. Using Coldwater's baby teeth as payment to enter, the two requested passage to the Underworld, clarifying that they wanted to come back afterward. The Dragon agreed but required a gift for her service, and Coldwater said they'd get her anything she wanted, but the Dragon revealed that her gift was that button in Coldwater's pocket.
When Coldwater asked if he could use it again, even if briefly, but Dragon refused, stating that the "first door" was still open. After obtaining the button, the Dragon told Coldwater and Wicker that they would have twenty-four hours to return, otherwise she would eat their bodies, and blew a gust of smoke at them, separating their souls before sending them to the Underworld.
Magic and Abilities
- Dragon Physiology: The Hudson River Dragon is a dragon. Dragons are an ancient race of mythical reptiles that possess vast abilities. She is able to open portals, as well as transport souls to the Underworld.
- Fire Breathing: The Hudson River Dragon is able to generate and release fire from her mouth, releasing smoke whenever she speaks.
- Soul Manipulation: By blowing smoke at others, the Hudson River Dragon is able to release their souls from their bodies, allowing them to travel to the Underworld.
- In The Magician King, the Grand Canal Dragon purchased the Button from Josh Hoberman in Venice, and later instructed Quentin Coldwater to find the "first door" to visit Fillory again.