Alvarez died Monday in London of pneumonia, according to his literary representatives, Aitken Alexander Associates.
Writing alternately as A. Alvarez or Al Alvarez, he had a long, productive and controversial career. He began as a highly influential critic, who as poetry editor of the Observer, was an early champion of Plath, her then-husband Ted Hughes, John Berryman and others he believed would enliven contemporary poetry. He would go on to write novels and poems and to complete nonfiction books about life "beyond the fiddle'' of the book world, whether rock climbing (''Feeding the Rat''), swimming (''Pondlife''), the search for oil in the North Sea (''Offshore'') or poker (''The Biggest Game In Town'').
"People were continually asking me, in so many words, what a literary guy who knew about poetry was doing in joints like these,'' he wrote in the memoir "Where Did It All Go Right?'' that was published in 1999. "I went because I realized very early that I would only get one shot at the planet, so I might as well see for myself what was on offer.''
On Tuesday, friends and admirers noted Alvarez's wide-ranging legacy, with some singling out ``The Biggest Game of Town'' for helping to popularize the World Series of Poker, which he covered in 1981. Fellow author and poker fan Jim McManus wrote on his Facebook page that Alvarez's book ``inspired many thousands of amateurs to play in that tournament, and quite a few journalists.''
Alvarez's breakthrough work, published in 1971, was his most painfully personal. In "The Savage God: A Study of Suicide,'' he traced the history of how society looked upon suicide _ from the centuries of being treated as a religious taboo, to glorification by the 19th-century Romantics to the randomness and plain despair of modern times.
Praised by Joyce Carol Oates in The New York Times as "provocative and exceptionally well-written,'' the book unintentionally helped launch a cottage industry in publishing: It opened with one of the first extended accounts of the final months of Plath, who in 1963 was been found dead at age 30 in her London kitchen after sealing the window and door, turning on the oven and sticking her head inside. Her death was ruled a suicide, although Alvarez would question whether Plath _ who had two small children _ had meant to kill herself.
In her lifetime, Plath was little known beyond fellow poets. But her fame rose through the 1960s thanks in part to the posthumous release of her "Ariel'' poems, many written in a cathartic and devouring rush after her marriage to Hughes collapsed in 1962. Alvarez was originally closer to Hughes, but spent more time with Plath after the couple separated and eventually regarded her as the greater talent.
In the book's most talked about section, Alvarez recalled Plath inviting him to her home on Christmas Eve 1962. She read to him poems from "Ariel,'' notably "Death & Co.,'' that left him awed and startled by her stark references to death and inescapable sense of finality. Alvarez didn't know what to tell her and departed even as, he would write, she sobbed and begged him to stay.
"She must have felt I was stupid and insensitive. Which I was,'' he recalled. "I knew I had let her down in some final and unforgiveable way. And I knew she knew. I never again saw her alive.''
Alvarez had wanted her to be known for her work, writing in "The Savage God'' that "The pity is not that there is a myth of Sylvia Plath but that the myth is not simply that of an enormously gifted poet whose death came carelessly, by mistake, and too soon.'' But his book and its passage about Plath's long, loosened hair and its smell ``sharp as an animal's'' helped raise speculation over whether he and the poet were lovers. Alvarez addressed the rumors in the 1990s when he told Plath biographer Janet Malcolm that ``Sylvia wasn't my style. She wasn't my physical type.'' In "Where Did It All Go Right?'' Alvarez wrote that after Hughes left, Plath needed ``someone to live with and take care of her.''
"I wasn't up to her despair and it scared me,'' he wrote, adding that he never ``kidded'' himself that changing ``from friend to lover would have made a lot of difference to her in the end.''
Alvarez's memories of Plath enraged Hughes, who accused his onetime friend of betraying their privacy that led to a yearslong estrangement. In a letter to Alvarez, Hughes dismissed the critic's contention that his revelations would end speculation about Plath's death and anticipated _ correctly _ a "whole new world of hypothesis.''
"Before this, the fantasies were hot air, blowing each other away as fast as they were invented, all of them perfectly weightless,'' Hughes wrote. "But now you have provided what seems to be substance, real fact and foundation _ the story from one who was in the room.''
In the 2003 film "Sylvia,'' which starred Gwyneth Paltrow as Plath and Daniel Craig as Hughes, Jared Harris played Alvarez.
At the time he knew Plath, Alvarez himself nearly ended his life. His first marriage, to Ursula Barr, was ending and he was haunted by childhood stories about his parents ``half-heartedly'' putting their heads inside gas ovens. He became so depressed that he swallowed 45 sleeping pills and fell into a coma. He awoke days later, and would look back on the experience as a death, and a rebirth.
"I began gradually to stir into another style of life, less theoretical and less optimistic, less vulnerable. I was ready for an insentient middle age,'' he wrote in "The Savage God.''
Alvarez married Anne Adams in 1966 and with her had two children. He previously had a son with Barr, the granddaughter of Frieda Lawrence, who was the widow of D.H. Lawrence, a lineage Alvarez would say compelled him to propose marriage. Alvarez wrote briefly about his first wife in "The Savage God'' and at length in the 1982 release "Life After Marriage,'' which Barr denounced in the London Review of Books as fiction, adding, "It is a pity he has neither the good taste, nor the talent, to present it as such.''
Alvarez was born in London, and as a young man he was drawn equally to adventure and contemplation, although contemplation at first won out. At Oxford's Corpus Christi College, he absorbed so much literary theory that he founded a campus discussion group called the Critical Society. He became poetry critic and editor of the Observer in 1956, but a decade later was bored of highlighting the creations of others. His epiphany, what he called his ``road to Damascus moment,'' came while reading ``Bleak House'' and becoming so "totally caught up'' that he didn't bother to analyze it.
"Here I am, a paid-up, card-carrying literary critic and I've forgotten that authors write books in order to give pleasure,'' he wrote in his memoir. "I must have known that when I first decided that writing was what I wanted to do with my life, and if years of churning out criticism have made me forget it, then I must give up criticism and get back to where I started.''