When the poet James Merrill (1926-1995) was born on the Upper East Side of Manhattan, his mother, Hellen, thought him tiny and ugly, even by newborn baby standards.

James weighed only 5 pounds 10 ounces. “Please, please, this is embarrassing,” Hellen said to her doctor. “Can’t you say 6 pounds?” When Hellen added that her son wasn’t very good looking, her maid stepped in. “Maybe not, Mrs. Merrill, but he has personality.”

These details are related in Langdon Hammer’s very fine if punishingly long “James Merrill: Life and Art,” the first biography of this important and complicated American poet. Hellen’s maid had spoken truth. James Merrill’s enormous personal charm helped him make friends everywhere he went, at all stages of his life. A gay man, he picked up lovers with similar ease.

At birth, he had more going for him than personality. Merrill was the son of Charles E. Merrill, the co-founder of Merrill Lynch. Vastly wealthy, the family had estates in Southampton, N.Y., and Palm Beach, Fla., and a penthouse at the Carlyle in New York City. This constant movement instilled in Merrill a primal restlessness. He was never in one place for long.