Pegasus

Pegasus was the form Helios took when he was on Earth, appearing as a white winged horse with a golden horn atop his head. His horn was really the Golden Crystal. He hid in Chibiusa's dreams, because he could only survive on Earth by living in someone's beautiful dreams. Chibiusa could communicate with him using the Stallion Rêve, and call for his help in battle with the Crystal Carillon.

Trivia

 * Pegasus is named after a winged horse in Greek mythology.