Aenar Targaryen

Aenar Targaryen was a dragonlord of the old Valyrian Freehold, who moved House Targaryen to Dragonstone right before the Doom of Valyria - which resulted in the Targaryens being the only family of dragonlords to survive the destruction of Old Valyria.

History
The Valyrian Freehold was a vast empire that ruled most of Essos, dominating half of the known world for millennia. About four centuries before the War of the Five Kings, however, the entire Freehold was destroyed in a single day by a cataclysmic volcanic explosion known as the Doom of Valyria. The fires were so hot that even dragons burned alive in mid-air, and the Valyrian Peninsula itself was rent asunder, with large sections falling into the sea, leaving behind a scattered chain of islands in the Smoking Sea.

All of the Valyrian dragons and their ruling aristocracy of Dragonlords were killed in the Doom - all but one family. Twelve years before the Doom, Aenar Targaryen led House Targaryen to settle the distant, western-most outpost of the Freehold: Dragonstone island, off the east coast of Westeros, across the Narrow Sea. The Targaryens therefore survived on Dragonstone while Valyria burned, and when the dust settled, they possessed the world's only remaining dragons.

Some say that Aenar decided to remove his entire household to such a far-flung outpost because his daughter had prophetic dreams about the impending Doom of Valyria. Others who are skeptical of prophecies and magic say that Aenar lost a power struggle with rival dragonlords in the heartland of the Freehold, and fled to Dragonstone in defeat - and that the story about his daughter's prophetic dreams was just a tale that grew up later to try to obscure their shame.

Whatever the case, one century later, Aenar's direct descendant Aegon I Targaryen conquered and united the mainland of the Seven Kingdoms using the last three Targaryen dragons.