To the Haida of the Pacific Northwest the Thunderbird is the most powerful creature. It is a mythological figure or spirit, just like the double-headed snake, Sisiul. The Thunderbird represents the sun and the upper world while the snake represents the moon and the underworld. When the Thunderbird flaps its mighty wings the mountains shake and the people tremble. Only the Killer Whale, the king of the sea and the strongest and largest of all living creatures can withstand the power of the Thunderbird. When they battle the sea rises and tidal waves plague the land.