Peter Matthiessen, a roving author and naturalist whose impassioned nonfiction explored the remote endangered wilds of the world and whose prizewinning fiction often placed his mysterious protagonists in the heart of them, died Saturday at his home in Sagaponack, N.Y. He was 86.
His son Alex said the cause was leukemia, which was diagnosed more than a year ago.
Mr. Matthiessen's final novel, "In Paradise," is to be published Tuesday by Riverhead Books.
Mr. Matthiessen was one of the last survivors of a generation of American writers who came of age after World War II and who all seemed to know one another, socializing in New York City and on Long Island's East End as a kind of movable literary salon peopled by the likes of William Styron, James Jones, Kurt Vonnegut and E.L. Doctorow.
In the early 1950s, he shared a sojourn in Paris with fellow literary expatriates and helped found The Paris Review, a magazine devoted largely to new fiction and poetry. His childhood friend, the late George Plimpton, became its editor.
A rugged, weather-beaten figure who was reared and educated in privilege -- an advantage that left him uneasy, he said -- Mr. Matthiessen was a man of many parts: litterateur, journalist, environmentalist, explorer, Zen Buddhist, professional fisherman and, in the early 1950s, undercover agent for the CIA in Paris. Only years later did Plimpton discover, to his anger and dismay, that Mr. Matthiessen had helped found The Review as a cover for his spying on Americans in France.
Mr. Matthiessen's travels took him to the wilds of Asia, Australia, South America, Africa, New Guinea, the Florida swamps and even beneath the ocean. They led to articles in The New Yorker and other magazines and a raft of nonfiction books, among them "The Snow Leopard" (1978), about a grief-stricken spiritual journey to the Himalayas, and "Men's Lives" (1986), about Long Island fishermen and their vanishing way of life. The paleontologist Stephen Jay Gould called Mr. Matthiessen "our greatest modern nature writer in the lyrical tradition."
Of his more than 30 books, nonfiction works far outnumbered the novels and short-story collections, but he considered fiction his first and highest calling.
"Nonfiction at its best is like fashioning a cabinet," he told The Paris Review in 1999. "It can never be sculpture. It can be elegant and very beautiful, but it can never be sculpture. Captive to facts -- or predetermined forms -- it cannot fly."
He holds the distinction of being the only writer to win the National Book Award in both fiction and nonfiction. And his fiction and nonfiction often arose from the same experience.
His fourth novel, "At Play in the Fields of the Lord" (1965), grew out of his reporting for "The Cloud Forest: A Chronicle of the South American Wilderness" (1961). The novel, set in the Brazilian rain forest, depicts the interaction between missionaries and tribesmen -- at one point Mr. Matthiessen, an early user of LSD, has his protagonist drink a native hallucinogenic brew -- and Western civilization's damaging impact on primitive peoples. A film adaptation directed by Hector Babenco was released in 1991.
Mr. Matthiessen's fifth novel, "Far Tortuga" (1975), was inspired by a New Yorker assignment in which he reported on the vanishing Caribbean tradition of turtle hunting. Highly experimental -- it drew on recordings of sometimes cryptic Caribbean dialogue -- the novel drew mixed reviews.
He delved into another isolated world for his late-career "Watson" trilogy -- "Killing Mister Watson" (1990), "Lost Man's River" (1997) and "Bone by Bone" (1999) -- parts of which he compressed into one long opus, "Shadow Country" (2008). It won a National Book Award, though many critics thought a reworked version of previously published fiction did not deserve the honor.
The trilogy uses the life and death of a fearsome historical figure, Edgar J. Watson, to address issues of race, environment and power in America. Watson, a mysterious cane planter in the Ten Thousand Islands region of southwest Florida, was suspected in dozens of murders, including that of the outlaw Belle Starr. Watson himself was killed in 1910 by residents of Chokoloskee, an island settlement where he was suspected in a string of deaths.
Peter Matthiessen was born on May 22, 1927, in New York, a descendant of Scandinavian whale hunters and the second of three children of Erard A. Matthiessen, an architect and conservationist, and the former Elizabeth Carey.