Ronald Searle, the British illustrator who dreamed up the raucous schoolgirls of St. Trinian’s and inspired a generation of cartoonists with his delicate pen stroke and irony, died Dec. 30 at a hospital in Draguignan, France. He was 91.

His literary agent, Rachel Calder, confirmed his death but said the cause had not been determined.

Mr. Searle was widely regarded as one of the 20th century’s finest graphic artists — a draftsman whose spidery pen-and-ink drawings revealed the hilarity and the ugliness of human experience.

He was best known in England as the cartoonist who created St. Trinian’s school, whose mischievous-to-criminal young ladies won the everlasting affection of the prim and proper British audience. In the United States, he drew dozens of covers for the New Yorker magazine. More than one of them featured self-satisfied cats.

Those popular works belied the bleak, and in many ways defining, undercurrent of Mr. Searle’s life. During World War II, he nearly died in a Japanese prisoner of war camp. Between forced labor and bouts of disease, he sketched his fellow inmates and their captors. There, he developed a deceptively simple style that would characterize his work for the rest of his career.

“I went into the war as an art student of 19, who did pictures of my mum and dad and the dog,” he once told the Spectator. “Suddenly you’re drawing people who are going to die. . . . The darkness in my drawings came from being a prisoner.”

Mr. Searle had created St. Trinian’s during the war, but the series did not take off until he returned to England from the internment camp. The girls’ exploits ranged from the quirky to the wicked. In one cartoon, a pointy-nosed schoolmistress chides a student for parading a hippopotamus through the academy’s vaulted halls. “Elspeth!” she shouts. “Put that back at once!”

In another cartoon, Mr. Searle drew schoolgirls looking upon the hanged body of one of their teachers. “Well that’s OK,” they say to each other. “Now for old ‘Stinks.’ ”

Mr. Searle tired of the series and tried unsuccessfully to destroy the school in a fictional nuclear attack. But spinoff films and books continued unabated. Colin Firth appeared in the latest movie adaptation, “St. Trinian’s” (2007).

In another popular series with a school motif, Mr. Searle created Nigel Molesworth, the wayward pupil of St. Custard’s. Nigel became the hero of “Down With Skool,” a book written by Geoffrey Willans and illustrated by Mr. Searle.

In one picture, Mr. Searle showed the school’s hapless athletes. The illustration was titled: “The football team played 8. Won 0. Drawn 0. Lost 8.”

Mr. Searle displayed a remarkable versatility over the course of his career. He drew the animated title sequences for the comedies “Those Magnificent Men in Their Flying Machines” (1965) and “Those Daring Young Men in Their Jaunty Jalopies” (1969).

In addition to his comics, Mr. Searle did a series of illustrations about European refugees in the late 1950s. In 1961, Life magazine sent him to cover the trial in Jerusalem of Nazi leader Adolf Eichmann.

He drew street sweepers, wrestlers and Coney Island revelers, all with the dry sensibility of an Englishman. In 1960, Life dispatched Mr. Searle to cover the Kennedy-Nixon presidential campaign. For a caricaturist, he once told the Independent, Nixon’s nose was an “absolute treasure.”

Mr. Searle’s prolific work for the New Yorker showcased his trademark droll style. In one cover from February 1973, he showed a gray cat seated at a table bearing a smorgasbord. The feline’s whiskers radiated like sun rays from its smug face. Above its head was a thought bubble showing how the cat saw the meal: a single fish.

Ronald William Fordham Searle was born March 3, 1920, in Cambridge, England. He began cartooning for the local newspaper as a teenager and attended art school at night.

In 1986, Mr. Searle’s war sketches were collected in the book “To the Kwai and Back.” He said that life in the POW camp was more harrowing than the depiction in the 1957 film “The Bridge on the River Kwai.”

Reviewing the book for the New York Times, cartoonist Bill Mauldin called Mr. Searle’s drawings “unforgettable.”

Mr. Searle’s first marriage, to Kaye Webb, a magazine and book editor, ended in divorce. His second wife, the former Monica Koenig, died in 2011 after 44 years of marriage.

Survivors include two children from his first marriage, John Searle of Spain and England and Kate Searle of London; and a grandson.