Few painters of modern times have received the honors and riches that came to Lucian Freud, the deeply talented and mysterious grandson of Sigmund Freud.

Often considered the greatest living master of the human form, Mr. Freud painted many hundreds of portraits that were seldom flattering but that revealed their subjects in searing, sometimes brutal honesty that might have made his grandfather proud.

But he wasn’t just the heir of the father of psychoanalysis. He managed to re-create and expand the tradition of classical portraiture in his paintings, which penetrated masks of pretense and seemed to pierce to the soul.

Mr. Freud, who died in London on Wednesday at 88, had found moderate success in Britain early in his career. He was a leading figure, along with Francis Bacon, in the London School of painters of the 1960s who concentrated on the human form.

It wasn’t until a 1987 retrospective at Washington’s Hirshhorn Museum that Americans began to notice the depth and power of Mr. Freud’s work. A new continent of art lovers was astonished by paintings that seemed to defy prevailing conventions, as well as time itself.

“They stop you where you stand,” Washington Post critic Paul Richard wrote at the time. “It is as if gravity itself had somehow been increased. . . . Freud’s pictures have a sense of time expanded, not easily explained. Anchored to the present, they seem to preexist the photograph.”

Time magazine critic Robert Hughes called Mr. Freud “the greatest living realist painter.”

From then on, despite frequent feuds with galleries and his reluctance to be interviewed, Mr. Freud became an art-world sensation.

He slathered paint onto canvases in thick layers of impasto, creating a brushwork style that seemed to echo the heaviness of the figures he represented. Girth deepened into gravity in a Freud portrait, and the disturbing grays, greens and purples blending with pinks and other flesh tones only added psychological depth to his figures.

Mr. Freud’s paintings have a rough incandescence, an oxymoronic ugly beauty from which people cannot avert their eyes — or close their wallets. In 2008, his portrait “Benefits Supervisor Sleeping” was sold by the New York branch of Christie’s auction house for $33.6 million — the most ever paid for a painting by a living artist.

Many of his works, including self-portraits, showed his figures in the nude — or “naked,” the term he preferred. He sometimes asked his subjects back for as many 80 sittings, coaxing them out of their clothes under a harsh light during intimate, all-night sessions.

Often irascible with the press, Mr. Freud could be charming and solicitous — almost therapeutic — to his portrait subjects. Posing for him, one model told Britain’s Express newspaper in 2008, it “felt like being an apple in the Garden of Eden. When it was over, I felt as if I had been cast out of Paradise.”

He often painted people with their pets, with the animals usually looking more dignified than their owners. His works were frequently very small — a 1998 portrait of a pregnant Jerry Hall, then the girlfriend of Mick Jagger, was four by six inches — but other portraits measured several feet across. Some of his famous subjects, such as Hall and model Kate Moss, were well known, but Mr. Freud more often portrayed his otherwise little-known friends, relatives and lovers, of whom there were many. He turned down requests from Princess Diana and Pope John Paul II, but he completed a portrait of Queen Elizabeth II in 2001.

“At one point I remember saying to [the queen], ‘You probably think I’m going in­cred­ibly slowly,” Mr. Freud told the London Times in 2006, “ ‘but in fact I’m going at 90 miles an hour and if I go any faster the car might overturn!’ ”

Lucian Michael Freud was born Dec. 8, 1922, in Berlin and went to England with his family in 1932. His father was an architect. Young Lucian saw a good deal of his celebrated grandfather while growing up and gave him some of his paintings. “I liked his company very much,” Mr. Freud recalled of his grandfather, who died in 1939. “He was never boring. He told me jokes.”

Mr. Freud served as a seaman in the British merchant navy during World War II and studied at several art schools. Although he sometimes pretended not to know their work, he was influenced by the between-wars tradition of such German painters as Otto Dix and George Grosz.

After his first gallery shows in the 1940s, Mr. Freud developed his signature style of thickly applied paint, coupled with an unsparing, straightforward gaze that exposed deep psychological currents.

In 1948, he married Kathleen Garman Epstein, daughter of sculptor Jacob Epstein. They had two daughters before their divorce in 1952. A year later, Mr. Freud married writer Caroline Blackwood, from whom he was divorced in 1958.

In recent years, it was revealed that Mr. Freud was a rake of epic proportions. He had at least 12 illegitimate children and, if the British press is to be believed, as many as 40. In his 80s, he was seen in the company of women who were young enough to be his granddaughters.

He often returned to museums to view the painters he considered his inspiration and, perhaps, his equals: Titian, Rembrandt, Ingres and Degas. Almost to the end, Mr. Freud remained a feverishly busy artist.

“I like it,” he said in 2006, “if people say very contradictory things about my work: ‘It’s very ugly.’ ‘It’s very beautiful.’ ‘Do you get your models from an asylum?’ ”