10. Moby Dick
The Myth: Moby Dick isn't a myth in the traditional sense of the word, as he's the bane of Captain Ahab's existence in his eponymous book by Herman Melville. Still, the idea of a vengeful and vindictive whale has permeated the modern zeitgeist as the target of one's obsession, which is mythical in its own right.
The Reality: In 1820, Captain George Pollard Jr., was in command of the Essex when it was sunk by a whale. He survived and returned to Nantucket, where he was given the Two Brothers to captain, but after two years, he crashed it on a coral reef and was thereafter determined to be unlucky at sea.
Pollard's troubles with the Essex came from an 85-foot albino sperm whale, which directly attacked and smashed into the ship. The whale returned to attack the vessel at greater speed, and the Essex began taking on water, leaving the men to flee. Pollard was away from the vessel when the attack occurred.
When he returned shortly after the whale slammed into the vessel a second time, he saw his first mate, Owen Chase, who told him, "we have been stove by a whale," and with that, the legend that would become Moby Dick was born.