Quicksilver, also known as Mercury, is Zelda's horse. His Hylain name is Argentum Vīvum. He is a white Clydesdale mix stallion with blue (walleye) eyes.
Quicksilver was born in a rural village close to Hyrule City Capital (Castle Town). This is where Zelda takes a rest from "city life" and rests in the countryside. He was going to be killed because he was too small to be a working horse. Zelda rescued him and payed top dollar to save his life. He grew and then became her Royal steed. He now lives a happy life.