From SF Scope:
Born in Philadelphia, Pennsylvania, on 30 January 1924, he was a children’s fantasy author for half a century (though he did also write several adult novels). He won the 1970 Newbery Award, and was a National Book Award Finalist, for The High King.
His books include three well-known series—The Chronicles of Prydain, The Westmark Trilogy, and The Vesper Holly Series—as well as at least 24 other books. His latest, The Golden Dream of Carlo Chuchio, is scheduled to be published by his long-time publisher, Henry Holt, in August 2007.
Before becoming the writer he’d always wanted to be, Alexander served in the US Army during World War II, working in intelligence. In 1946, he married Janine Denni, who predeceased him by two weeks.
His Prydain Chronicles were (and are) head and shoulders above most YA fantasy. I read them multiple times, and I’m quite certain they’ve influenced my own fiction ever since.