Haku

His real name is Nigihayami Kohaku Nushi but you can call him Haku for short. Although he has the appearance of a thirteen-year-old boy, he actually is the spirit of a river with a dragon form that can fly and do other cool stuff.

He gets trapped by Yubaba and made to be her apprentice and do her dirty work, until Chihiro comes along and saves him.

Haku once saved Chihiro from drowning in his river, which is coincidently called the Kohaku river.