Artistic communities have rarely been celibate or sober, but even by those standards Modigliani was a bohemian par excellence, an enthusiastic imbiber of alcohol and drugs with a succession of fiery relationships. His excesses were such that Picasso eventually wearied of them and the two colleagues drifted apart, although when Modigliani died in 1920 at the tragically early age of 35, Picasso did attend the funeral.
But now their friendship, as immortalised in paint, will be one of the highlights of the first exhibition of Modigliani's paintings in Britain for more than 40 years, at the Royal Academy in London.
The exhibition will bring together up to 60 works of the more than 300 authenticated Modiglianis, some of which have not been seen in public for decades, from private and public collections from Honolulu to South America and Japan. Among them will be the biggest gathering of his famous nudes probably ever seen. The show will examine the myths surrounding an artist whose distinctive elongated portraits and nudes have made him instantly identifiable to anyone with a vestige of an interest in art.
Modigliani was born into a cultivated Jewish family in Livorno, Italy, in 1884, where his father was an unsuccessful businessman and his unconventional mother ran an experimental school. He studied art in Florence and Venice before moving to Paris where he quickly got to know everyone and they him. He painted Picasso and Rivera, and the Spanish Cubist Juan Gris, in addition to dealers such as Paul Guillaume and Leopold Zborowski, as well as assorted girlfriends and models.
He and Picasso certainly knew each other well, having met when Modigliani first went to Paris in 1906 and lived in Le Bateau-Lavoir artistic community, where Picasso also had a studio and was working on works such as Les Demoiselles d'Avignon.
As well as sitting for Modigliani, Picasso owned several works by him, including Girl with Brown Hair, dating from 1918, which is being lent to the Royal Academy by the Musée Picasso in Paris. The Picasso portrait by Modigliani, which was owned by Picasso at one point in the 1930s, is being lent from a private collection.
Both artists shared an interest in African art, which influenced their respective work. Picasso is reported to have once said that Modigliani was the only man who knew how to dress and he tried to help him get a dealer.
But it appears they drifted apart. "From what one knows, it seems that after a while Picasso found him a bit tedious, with all the drinking and the drugs. He didn't approve of his lifestyle very much," Simonetta Fraquelli, the London exhibition's curator, said.
Modigliano indulged in the bad behaviour that had long been romantically regarded as quintessentially artistic. His rows with his girlfriends were legendary in the streets where he lived. André Salmon, the writer and critic, described him as dragging one along by the wrist "like a madman, crazy with savage hatred".
And he was widely regarded as uncouth, although with some suspicions that his bad-boy reputation was calculated. Picasso once suggested that he was only ever drunk centre-stage: "It's odd but you never see Modigliani drunk anywhere but at the corners of the Boulevard Montmartre and the Boulevard Raspail."
Beatrice Hastings, a South African-born English writer who was one of Modigliani's partners for a while, described him as both "a swine and a pearl" and recalled later in life how he was smoking hashish and drinking brandy when they met in 1914. He "never completed anything good under the influence of hashish", she said.
The artist could not stand the influential French artist and writer Jean Cocteau, who also frequented the same circles of the time, but, she said, had respect only for Picasso and the poet Max Jacob.
Modigliani's only solo exhibition in France, in 1917, was closed by police officers shocked at the nudes hanging in the window, creating a scandal that added to the artist's reputation.
But Ms Fraquelli said that one of the common myths around the artist - that he was largely ignored in his lifetime - was not true. He showed in many group exhibitions in Paris, including alongside Picasso, as well as in London, where in 1919 the writer Arnold Bennett paid so high a price for a painting that Modigliani and his final partner, Jeanne Hébuterne, were finally able to move into their first real home, an apartment in the Rue de la Grande Chaumière, immediately above one once occupied by Gauguin.
The period when Modigliani was living in Paris - which overlaps with the final years now being explored in the Degas, Sickert and Toulouse-Lautrec exhibition at the Tate Britain - was one of enormous excitement in France.
"Every aspiring artist made his way to the Mecca that was Paris," Ms Fraquelli said. "There was an explosion of artists in Paris, people coming from eastern Europe, from Spain, from Italy. Paris was the capital of art. It was a bit like coming to London now; there was a lot going on."
Yet it all ended in tragedy for Modigliani. A combination of infection and alcohol and drug abuse left him fatally weakened. About a fortnight after celebrating new year in style, he was was discovered by neighbours delirious and suffering from tubercular meningitis. He died on 24 January 1920.
Jeanne, by whom he already had one child and who was expecting a second, killed herself a day later, by throwing herself from her parents' fifth-floor apartment.
While not exactly debunking the many stories about Modigliani, Ms Fraquelli at least aims to resurrect his reputation as an artist. "The myths that surround him have somewhat clouded our view of his art. He certainly did live the bohemian life, there's no doubt about it, but he also painted a lot of wonderful paintings," she said.
"So much has been written about his dissolute bohemian life in Montparnasse that less work has been done looking at his art in its context. He is an artist who has had enormous popular appeal; he's an artist who fires the public imagination, but in terms of art criticism he hasn't been looked at so closely."
Serious academic research is now being carried out among writings of the period to fill in gaps in the records and augment the little that Modigliani himself seems to have written about his work. A new catalogue, including some works thought lost but newly traced, will be published to coincide with the summer exhibition.
Norman Rosenthal, exhibitions secretary at the Royal Academy, said: "People have always been slightly snobbish against Modigliani, but he was part of the intellectual artistic milieu of Paris and was taken seriously by everybody from Picasso downwards.
"He was a very clever person and his contribution as a portraitist is really unique. There's no one who quite tries to develop the idea of Modernism through portraiture and through the nude as he does."
Modigliani was close to the Cubist circle of Picasso, but while his paintings in the period from 1914 to 1916 were almost geometric in form, he never entirely embraced Cubism in his art. "He never breaks down the image in the way Cubism does; he never fragments his image," Ms Fraquelli said.
Confronted with the anti-Semitism of France, he also forged friendships with the large circle of Jewish artists in Paris, many of whom had arrived from eastern Europe, though they seemed less influential on his work.
Ms Fraquelli said he seemed as much inspired by the Italian classical tradition of Giorgione and Titian as anything. "He was very conscious of the art of the past and he had had a classical training in Italy."
His untimely death leaves the experts speculating what he might have produced had he lived. But dying young certainly appears not to have harmed his sales at auction houses, where one Modigliani sold not long ago for more than $30m (£17m). There is also an alarmingly thriving trade in fakes. And in exhibitions in Europe and America, his reputation has been re- examined in recent years in a number of significant shows.
Now Britain is finally to catch up. Thirteen years after 134,000 people visited the Royal Academy to see a collection of Modig-liani drawings that belonged to Paul Alexandre, his first great patron, Norman Rosenthal believes the paintings will be an enormous success. "We've been looking to do this for a while and we expect it to be a blockbuster. He's a blockbustery sort of artist."
"Modigliani and his Models" will be at the Royal Academy of Arts, London, 8 July to 15 October 2006