Of all the 20th-century British painters, it is Francis Bacon who best conveyed the new and confusing ways that century found to inflict pain. With his paintings of howling heads and spatchcocked figures, he caught the torturous physicality of the times through his preferred mode of expression: distortion. “The job of the artist is always to deepen the mystery,” Bacon once remarked. Nearly 30 years after his death, two vastly different volumes on the artist highlight the potency of that enigma.

For Mark Stevens and Annalyn Swan, two Pulitzer Prize-winning American arts journalists, Bacon has been a decade-long obsession. And with Francis Bacon: Revelations, an 800-page tome, they are clearly aiming for the definitive biography. Bacon, however, proves an elusive prey. “He sometimes seemed pulled in opposite directions,” the pair explain. “Explosive or restrained; bestial or civilized; masked or revealed; raw or cooked.”

Bacon was born in 1909 into a semi-grand Anglo-Irish family — his namesake, the Renaissance philosopher, was a distant ancestor — and spent his youth in the country houses of County Kildare. Childhood experiences would bleed into his later paintings, characterised by what his biographers describe as a “sense of simmering violence and foreboding”.

His father — “the major” — had a taste for foxhunting and arguments. It was his mother’s side of the family, whose steel business enjoyed a roaring trade in cutlery and artillery, who had the money.

Francis was something of a disappointment, “the runt of the litter” as Stevens and Swan note. He was asthmatic, with a “high flutey” voice and a penny-shaped face. And he liked boys.

There was little formal education, bar a spell in a minor public school in Cheltenham, but Bacon was a life-long autodidact. Crucially, he taught himself to paint. Going his own way didn’t extend to paying for it, however. Until he was well into his forties he lived off his mother and older men, and retained the services of his former nanny, who would oversee his gambling parties in South Kensington.

The artist’s little known prewar years have been illuminated by the authors. Periods in Berlin and Paris introduced Bacon to the work of the European Modernists, after which he spent an improbable period as an interior designer, arranging rugs and calfskin pouffes. Meanwhile, he courted the friendship of established painters such as Roy de Maistre and Graham Sutherland.

The war changed his fortunes. Bacon briefly served in the Air Raid Precautions service, but spent much of the war living quietly in a cottage in the grounds of Bedales, a boarding school in Hampshire (his asthma precluded him from active service). In the late 1940s and through the 1950s, his paintings of screaming popes, tormented businessman and crucifixions suddenly had an awful relevance. His blurry works, influenced as much by photography as Rembrandt and Velázquez, turned men into cuts of meat. If not enjoyable, they were now at least understandable.

Bacon’s colours — citrus shades of orange and green, bruising pinks and purples — were shocking to an audience immersed in the ashen palette of postwar London. A similar vibrancy accompanied his antics in Soho — a cycle of wine, wit and mishaps — where he could be benevolent company to friends such as Lucian Freud and a drunk hustler to others. He oscillated between alcohol and sedatives and treated his gallerists and patrons like cashpoints. His erratic behaviour created some delicious comedy. When Bacon unveiled his portrait of Cecil Beaton, the society photographer almost fainted. He had been turned, wrote Beaton, into “a severe case of elephantiasis”.

Bacon maintained a messy studio and an even messier love life. First, he was infatuated with a louche jazz pianist named Peter Lacy, who once threw him out of a window. And then came George Dyer, a petty thief, loosely associated with the Kray twins, with whom Bacon spent the 1960s. That ended bleakly in 1971, when Dyer overdosed in a Paris hotel bathroom on the eve of Bacon’s gala show at the Grand Palais. So as not to upset the celebrations, it was decided to deal with the body after the opening.

The biographers don’t entirely unpick the psychology of a man who could go to a champagne reception while his dead lover sat slumped on a lavatory. But, although generous to their subject, Stevens and Swan have succeeded in creating an incomparable resource for art historians, dealers, curators and collectors.

Bacon’s final days, spent in a hospital bed in Madrid in the spring of 1992, are the subject of Max Porter’s mercurial novella The Death of Francis Bacon. In an odd hybrid of poetry and fiction, seven imagined “written pictures” present staccato studies of the artist’s scattered thoughts as the end nears. “I can’t resist an unholy facial marriage,” reveals the bedbound Bacon about his macabre approach to composition. “I folded the head over at the eyes and laid it on the injury.”

Porter’s previous books, including the Booker Prize longlisted Lanny, have dealt with family and folklore. Here he takes stock of a talent — all the grudges, regrets and glories — in a kind of fever-dream. Flitting between the first and third person, Porter jumbles the artist’s morphine-fogged memories with premonitions about his legacy. There are dazzling passages but, ultimately, fragmented prose about fragmented pictures feels like a shard too far.

“The century abandoned me at dusk,” writes Porter in Bacon’s plaintive intonation. Time has passed, but on the page, in non-fiction or flights of fancy, the painter still mystifies. He remains an unfinished work.

Francis Bacon: Revelations, by Mark Stevens and Annalyn Swan, William Collins, RRP£30, 880 pages

The Death of Francis Bacon, by Max Porter, Faber, RRP£6.99, 80 pages

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