Patrick O'Brian, 85, a lifelong writer and translator who led a modest and reclusive existence in a French village until the early 1990s, when his series of Napoleonic-era sea stories was discovered by American readers and made him a cult figure, died Jan. 2 at a hotel in Dublin.

The cause of death was not disclosed. A resident of the fishing village of Collioure, in southwestern France, he was wintering at Trinity College in Dublin.

Mr. O'Brian will be best remembered for a series of 20 novels he wrote about Britain's sea war with Napoleonic France featuring Jack Aubrey, a true fighting sailor whose career proceeds from commander to flag rank, and his great, brilliant and mysterious friend, Stephen Maturin--an Irish-Catalan surgeon and naturalist who is a British intelligence agent.

The first volume of the series, "Master and Commander," appeared in 1969 and the 20th, "Blue at the Mizzen," was published last year. Mr. O'Brian, who had announced that he had always intended to end the series with the 20th book, revealed last month that he was working on a 21st Aubrey-Maturin novel.

The popularity of the series grew slowly. The books, largely unpublished in this country, sold sluggishly in Britain--despite lavish praise from such writers and critics as Graham Greene, A.S. Byatt and Iris Murdoch. His later fans included Eudora Welty. Mr. O'Brian's work was compared to such writers as Jane Austen.

Then, in 1991, an essay on the front page of the New York Times' Sunday book review section hailed Mr. O'Brian as one of the great unknown writers of his generation and praised his naval series as both great writing and great sea yarns.

W.W. Norton began bringing out new volumes of the series in hardback and the older volumes in attractive trade paperback editions. To date, the series accounts for the sale of more than 2 million books, with all of Mr. O'Brian's later volumes appearing on national bestseller lists on both sides of the Atlantic.

The series made something of a star of Mr. O'Brian, who packed large halls for a series of lectures he gave in this country. The series also spawned everything from calendars to a cookbook featuring the strange, exotic and, at times, frankly revolting dishes the two friends consumed in the course of their worldwide adventures.

Other books aimed at Aubrey-Maturin fans included atlases, to better follow the action; lexicons that explained arcane seagoing terminology that could trip up the landlubber reader; and a book on the music the two friends loved and played aboard ship. Norton also published a newsletter to keep fans informed of the progress of the series and the life of Mr. O'Brian.

In one regard, Jack Aubrey followed in a long tradition. There have been numerous fictional series dealing with Britain's Royal Navy fighting Napoleon. These included C.S. Forester's Horatio Hornblower, Alexander Kent's Richard Bolitho and Dudley Pope's Nicholas Ramage. Mr. O'Brian's work simply carried the genre to another level.

The Aubrey-Maturin series not only told the story of the British navy and the geopolitics of the Napoleonic world, but also was a chronicle of an entertaining, unusual and highly unlikely friendship between two men. Aubrey, a large blunt man who was as English as roast beef, was something of a mathematician and a perfect sailor and warrior--he was born to command a ship of war. Maturin, a brilliant surgeon and world-class naturalist, also was a gifted linguist and accomplished spy.

The two things the friends seemed to have in common, aside from the high regard in which they held each other, were their love of music (one played the violin, the other the cello) and their almost comical incompetence in dealing with normal life ashore, including their families and especially life with women. While broadsides and political bedlam held no fear for the duo, a seemingly long line of women caused them to beat retreat and almost flee to the sea.

The series gained its following for its portrayal of the interaction of the two friends and their crew mates. The action inevitably results in a "butcher's bill" that requires the services of Dr. Maturin, with the reader graphically informed just how the sick and injured were treated in the beginning of the 19th century.

The friends are hardly perfect. Aubrey, all but a buffoon on land, where he lacks both money and luck, is a married man with a wandering eye for the ladies. Maturin, who spends part of the series as a champion and user of various narcotics, is totally "at sea" aboard ship. If the reader feels lost at nautical terms and goings on, Maturin is worse.

In one comic scene, the good doctor even manages to trip and fall overboard in a calm sea. He was rescued by a captain and crew fighting to keep straight faces. In another first for a secret agent, Maturin is attacked by a platypus, which turns out to be no laughing matter.

Mr. O'Brian was born Richard Patrick Russ in Buckinghamshire, England. His father was a physician who specialized in the treatment of gonorrhea. Mr. O'Brian, who kept much of his life secret until 1998, was a sickly youth, with chronic respiratory disease, who read a great deal about history and the natural sciences.

Despite his illnesses, he also took to the sea, where a family friend taught him to sail.

He published his first two books, about animals, as a teenager.

In World War II, he drove ambulances during the London Blitz and later served in British intelligence organizations, including the Special Operations Executive. He served in London and worked on propaganda radio broadcasts to occupied Europe.

In 1945, after publishing three novels and a volume of short stories under his real name, he changed his name to Patrick O'Brian. After the war, he returned to writing, once saying that he never contemplated any other life. He lived in Wales before moving to France, where he had lived since 1949.

His lack of financial success as a novelist was offset by his gifted translations of such writers as Simone de Beauvoir and Andre Maurois. He also wrote a well-received biography of his friend, the painter Piccaso. Another of his biographies was of Joseph Banks, the famed British naturalist who traveled with British Capt. James Cook to the Pacific. In 1956, he published his first sea novel, "The Golden Ocean," which told of an expedition to the Pacific.

His first marriage, to Sarah Russ, ended in divorce. He had two children from that marriage, a daughter, Jane, who died at age 3 of spina bifida, and a son, Richard Russ, who is writing a biography of his father.

In 1945, he married Frieda Mary Wicksteed Tolstoy-Miroslavska, whom he met while both were working in the Blitz. She died in 1998.

In addition to his son, survivors include a stepson, the historian Count Nikolai Tolstoy-Miroslavsky.