In the Brothers Grimm tale “The Golden Bird,” a fox helps the youngest prince complete his quest.
The king discovers that a golden apple disappears from a tree each night and sends his sons to find the thief. The youngest prince listens to the fox’s advice, unlike his older brothers, and eventually encounters the golden bird. His journey expands to include a golden horse and a golden princess.
The fox repeatedly gives practical instructions, warning the prince not to exchange a plain object for a splendid one or enter a palace at the wrong time. The prince’s success depends on following this advice exactly. His older brothers, by contrast, ignore or exploit the guidance and suffer consequences.
The fox is later revealed to have a human form that can be restored through a specific act. This transformation is a separate final episode, not the source of the golden bird itself.