Born Alyn of Hull on Driftmark a year after his brother Addam, to Marilda the shipwright's daughter, who claimed both boys had been fathered upon her by Ser Laenor Velaryon, though Mushroom in his Testimony says it was Lord Corlys himself. After Addam claimed Seasmoke in the Sowing of the Seeds, Lord Corlys had both brothers legitimized and made them next after his slain trueborn grandsons in the Velaryon line, and after Addam fell at the Second Battle of Tumbleton it was Alyn alone who carried his grandfather's name into the years after the Dance. He took ship at the age of fourteen against the Triarchy in the Stepstones during the Daughters' War, smashed their fleet to splinters there, and came home with the name Oakenfist that would be his for all the rest of his life.
Lord of Driftmark upon the death of the Sea Snake in 132 AC, he wed Lady Baela Targaryen, the wilder of Prince Daemon's twin daughters, and got upon her a daughter Laena who became Lady of the Tides after him. But Alyn could not be kept long ashore; he sailed six great voyages out of Driftmark across the ensuing decades and saw further of the world than any Westerosi captain in his age except his own grandfather. In 157 AC he commanded the fleet that broke the Planky Town for King Daeron I's Conquest of Dorne, sweeping halfway up the Greenblood while the king's host engaged the Dornishmen in the Prince's Pass, and was made Master of Ships for it. Twice his ships brought home a captive king Viserys II, on whose release he had himself negotiated from Lys. Of his lovers, the most beloved was Princess Elaena Targaryen, who bore him twins, the bastards Jon and Jeyne Waters, before he disappeared at sea on his last voyage; the boy Jon, knighted and wed in time, would father the trueborn son who founded House Longwaters.