Cygnus, the swan:

Cygnus is one of the largest and easiest to find constellations in the night sky. It is also one of the few constellations that actually resembles its namesake. The constellation represents the youth Cygnus who was a friend to Phaethon, the son of Apollo. Phaethon attempted to drive Apollo's chariot (the Sun) across the sky one day. He lost control of the horses and was shot out of the sky by one of Zeus's thunderbolts before he could do anymore damage to the earth. Phaethon landed in a river, and Cygnus kept diving into the river like a swan in order to find his friend. Zeus was so impressed by Cygnus's loyalty and friendship that he turned the youth into a swan and placed his image into the night sky. The bright star Deneb is one of the three stars (along with Altair and Vega) that comprise the asterism known as the "Summer Triangle". Cygnus is visible throughout the summer and well into the fall.