STALIN came to love life lived in the twilight, and Simon Sebag Montefiore argues that the "world apart" of konspiratsia was the crucial formative experience of his life. Born Josef Djugahsvili, this son of a feckless Georgian cobbler and a proud, onward-urging mother may have been an autodidact, feasting as a teenager on forbidden books smuggled into the Tiflis Seminary (French novels as well as Marxist treatises). But instead of joining the priesthood he became a terrorist-gangster mastermind who arranged bank-robberies (or "heists", as Montefiore likes to call them), hijackings of mail ships, raids on government arsenals and the extortion of oil millionaires in the Black Sea port of Batumi and the Caspian Sea port of Baku.

All proceeds of his crimes during the first two decades of the 20th century went to the Bolshevik Party cause, for beyond a fondness for wine and a dandyish interest in clothes (spurred by a chameleon-like need to keep shedding and adopting disguises) he exhibited an ascetic demeanour. His coolness and his self-assurance meant he had several narrow escapes, outwitting the various "spooks" detailed to follow him. He once said he was "like quicksilver" and so Montefiore likens him to "Macavity, TS Eliot's elusive cat".

Lenin called him his "wonderful Georgian" and it flattered him to be known to some as Koba, after the romantic bandit-hero of a Caucasian novel.

When inside prison he would seek out the company of professional criminals, preferring their company to that of his fellow intellectuals. But outside prison his most consistent role was as the uninvited guest, if not always the unwanted one. He was ready to doss on the floors of friends and strangers, though he often managed to snaffle a bed, rarely sleeping in the same place for long.

Usually he proved to be good company for the duration of his visit, carousing and singing and reciting poems but also eyeing any daughters of the house . . . the younger the better . . . with a predatory twinkle.

Montefiore is apt to use the terms "psychopathic" or "semipsychotic" rather loosely, even when describing Stalin's chief "enforcer and cutthroat" Simon Ter-Petrossian, known as Kamo.

But he is careful to avoid applying any such term borrowed from clinical psychology to define Stalin's villainy. Instead, he resorts to the trope of the loner shorn of conscience. At times Stalin resembles an existential anti-hero, whose murderous appetite seems almost casual rather than vicious. While eschewing all sentiment, he was also given to such haphazard and unmediated acts of kindness and indulgence as seem to accompany the corruption of absolute power.

He was a lyric poet (a Shropshire lad in Georgia) and Montefiore introduces each part of the book with one of his poems.

"You'd have made a great priest, " a qualified priest tells this charming, pockmarked troubadour at one point. Lenin, for all his patina of gracious nobility, comes across as the nastier personality, yet we know that Stalin would become the more accomplished mass murderer. He did not so much wash the blood from his hands as wash his hands in that blood.

Not only did he graduate as an atheist while studying for the priesthood, but also his experience of the repressive atmosphere in the seminary may have been at the heart of his own later urge to repress others. Beguiling, impregnating and abandoning women was a forte. Although it is impossible to prove, Montefiore offers plausible reasons for thinking that Stalin may have fathered the first of his several bastards in 1899. He also thinks he may have pinpointed the first instance where Stalin ordered someone's death, as early as 1901.

With the aid of a printing press for publishing Bolshevik leaflets (in both Georgian and Armenian) and grenades, his "Mauserists" terrorised capitalist employers and police throughout the Caucasus, the 1907 Tiflis bank heist being the most newsworthy of his spectaculars. But in 1917, he would develop calluses on his fingers from writing so frantically for Pravda, which he edited. Stalin was unusual, being "as adept at debating, writing and organising as he was at arranging hits and heists", writes Montefiore. "The command, harnessing and provocation of turmoil were his gifts."

Most Tsarist exiles were holidays for left-wing intellectuals . . .

one is amazed at how leniently these sulphurous future revolutionaries were treated . . . and up until 1915 Stalin had enjoyed a series of languorous sojourns, with their picnics and mock trials and debates, their frenzies of reading and their playful opportunities for escape. But Stalin's last exile was in the bitter-cold conditions of the distant, sub-Arctic Siberian province of Turukhansk, where winter temperatures dropped to minus 60degrees Celsius. In Kureika, a small village of 67 persons living in primitive shacks, Stalin still managed to emerge as the alpha male, acquiring skills as hunter and fisherman and taking as his mistress a 13-year-old peasant girl, whom he twice made pregnant. In Montefiore's estimation, this period was crucial to Stalin's warped development: "Perhaps Siberia froze some of the Georgian exoticism out of him. He brought the self-reliance, vigilance, frigidity and solitude of the Siberian hunter with him to the Kremlin."

Montefiore is occasionally guilty of introducing phrases in quotation marks without indicating their source. His punctuation is often wild (for which his copy editor must share the blame), his phraseology sometimes rather crude and his fondness for cinematic allusions excessive.

Nonetheless the overall impression is one of Carlylean energy, or even incontinence, with his prose torrenting along. For as much as he offends with the odd lumpen phrase, he dazzles with others. For example, he talks of Stalin's "feline charisma" and his "Bedouin informality", declaring him an "expert at riding the random".

There is certainly no denying the doggedness of Montefiore's research or indeed his resourcefulness: he relies heavily on the archives of the Georgian Filial Institute of Marxism-Leninism, which had been closed until he persuaded the Georgian president to allow him access to them. This treasure trove yielded up the memoirs of Stalin's mother among the memoirs of numerous family members and early friends and acquaintances, several of which had been written before the Terror and were thus unbowdlerised.

In relation to this I must praise Montefiore's use of the footnote, that forgotten authorial art.

Thus he is able to maintain an intriguing commentary on sources as well as to cast forward glances to the mostly unfortunate fates of Stalin's familiars and associates. Although there is an excellent epilogue, it is helpful to know these things as the story unfolds and before individuals are lost in the confusion of similar-sounding Caucasian names.

On practically every page of Young Stalin there is a reason to smile with satisfaction at the thrust of revelation, and often a reason to gasp or even to chuckle.

As quasi-academic populist biography goes, therefore, this is as good as it gets.