We will never know who was Stalin's real father. The paternity of great men is often steeped in mystery. In Stalin's case, it was even suggested that Emperor Alexander III was his real father. Another candidate was a gay aristocratic Russian explorer. Neither of these two is a convincing can didate, but Stalin himself, a self-made man in every sense, liked to imply sometimes that his natural father was not his official one. But in his home town of Gori, in Georgia, there were in fact four very plausible candidates, including his official father - but of these four, only one, Koba Egnatashvili, remained in his life as a sort of foster parent.

Until now, his story has never been fully told. There were no photographs of him and most biographies simply repeated the inventions of other sensationalist historians. Yet the truth is more bizarre still, for this other family became the most trusted part of Stalin's court right up until the 1940s. Indeed, his possible half-brother became his NKVD food taster nicknamed "the Rabbit". It is a connection even more extraordinary because under the Rabbit served a young chef who would become the grandfather of another secret police officer: Vladimir Putin.

Stalin was born Josef "Soso" Dzhugashvili on 6 December 1878 (not 21 December 1879, his official birthday) to Beso Dzhugashvili, a cobbler, and his pretty and strong-willed wife, Keke. Beso was soon to become a wife-beating and child-beating alcoholic, tormented by rumours in the town that he was not Stalin's real father. Keke was determined that Stalin should receive a priestly education so that he could become a bishop. Beso, who had been helped throughout his career by a local hero named Koba Egnatashvili, a legendary wrestling champion, wealthy local merchant, wine dealer and owner of a successful tavern, wanted him to become a cobbler. And now we have a photo of this virile Georgian who was to play such an important part in Stalin's life.

When Beso became such a drunken embarrassment that he was known in the town as "Crazy Beso", Koba Egnatashvili helped Keke by finding her work, feeding Stalin and helping pay for his education at the church school and later at the seminary of Tiflis.

But he was not the only local man of power who aided young Stalin: Keke was also helped by the local priest, Father Charkviani, and the local police chief, Damian Davrichewy, both of whom were also said to be Keke's lovers. Indeed, Stalin himself, who encouraged mystery about his own origins to embellish his mythology as a great man, told several people that he was the son of this priest. The police chief's son later claimed that his father was Stalin's real father. But Stalin also implied to several people that Koba Egnatashvili was. He certainly worshipped the rich wrest ling cha m p ion: he was still talking about him 70 years later. When he became a revolutionary, he paid Koba the great compliment of adopting the name "Koba" as his own nom de guerre.

We will never, of course, know who was Stalin's biological father. In my book Young Stalin, I lean towards Crazy Beso simply because there is no conclusive evidence otherwise. But Koba Egnatashvili was actually the closest thing Stalin had to a father figure. It is also quite pos sible that Koba was indeed the biological father, for Keke, perhaps innocently, perhaps leaving a portentous message for posterity, admits in her memoirs that "Koba Egnatashvili helped us in the creation of our family".

As Stalin grew up, Koba certainly took the place of his real father. It seems that he loved little Stalin, and the affection was repaid. Stalin never lost his respect for him, and remained a somewhat mysterious part of the Egnatashvili family. While Crazy Beso beat the child and terrorised Stalin and several times kidnapped him from school to force him to train as a cobbler, Koba protected him, funded him and helped him in many ways. He may not have been Stalin's real father, but he acted like a father to him.

When Stalin left Gori to become a revolutionary in an adventurous career as terrorist mastermind, gangster godfather, poet, pirate, bank robber, Marxist fanatic and Bolshevik org aniser, he kept in contact with the Egnatashvilis. This was somewhat ironic, as the Egnatash vilis were prosperous capitalist entrepreneurs. Koba's two sons, Sasha and Vaso, were given expensive educations at a Moscow gym nasium (high school). Even after the Bolshevik (October) revolution in 1917, the family prospered as "Nepmen" (private businessmen) during Lenin's economic compromise with capitalism. They ran a chain of taverns and restaurants in Baku and Tiflis, in today's Azerbaijan and Georgia. Old Koba died in 1930 in his eighties, but in 1928 Stalin had executed his "Great Turn" leftwards, ending Lenin's New Economic Policy and embarking on a ruthless drive to fund industrialisation by collectivising the peasantry.

Ten million innocent people were shot or died of hunger. The Egnat ashvili brothers lost their taverns and were arrested. But Vaso managed to convince local officials that he had to speak to Stalin in Moscow, and so, while his brother remained in jail, he headed to the capital. Through the good offices of Abel Yenukidze, an affable Georgian womaniser and top Bolshevik official, Vaso was received by Stalin who immediately ordered that the two brothers be freed and summoned them to Moscow.

Even though neither brother had been a socialist, let alone a Bolshevik, Stalin needed trustworthy henchmen around him. Besides, he had grown up with the Egna tashvili boys and loved their old father. Amazingly, he made Sasha a secret police officer in what became, in 1934, the dreaded NKVD, while Vaso became his eyes and ears in his homeland, Georgia, first as a newspaper editor and later as secretary to the Georgian central executive committee. The Caucasus was then ruled by the fast-rising young Stalinist henchman Lavrenty Beria, but Stalin liked to keep up his own sources of information in the south: Vaso always had direct access to Stalin, which infuriated Beria. And everyone in the NKVD soon knew (and whispered) that the Egnatashvili brothers were not just Georgian favourites: they were Stalin's half-brothers.

As for Sasha - a genial, handsome athlete and a wrestling champion like his father, Koba (as his photograph on page 35 shows) - he became a powerful courtier at the court of the Red Tsar. He enjoyed a special position because, although he was an NKVD officer, he served with the independent Kremlin security guards, which Stalin, cautious and paranoid about his security, kept under separate command even though it was nominally under the secret police, the People's Commissars for Internal Affairs.

When Stalin unleashed the Great Terror in 1936, he became ever more sensitive about his own security: he promoted Sasha to command the secret world of his food supplies and the country houses where he actually lived. So Sasha the successful restaurateur became master of dictatorial feasting and luxury.

I had read in various sensationalist books on the secret police that Sasha Egnatashvili was nicknamed the Rabbit because he actually became Stalin's food taster. This was one of those rumours that I discounted as being too outré: however, it turned out to be true. Indeed, Sasha soon became a very important courtier, always present in the background wherever Stalin went. Whether Stalin was holding huge banquets at the Kremlin for foreign visitors such as Ribbentrop in 1939 or Churchill in 1942, or just private dinners at his own villas for Politburo magnates, the Rabbit was in charge and, at smaller dinners, he often joined the company.

Among the Rabbit's staff at Stalin's villas was an experienced and trusted cook who rather extraordinarily had served Rasputin and Lenin, and now cooked for Stalin, too. This was President Vladimir Putin's grandfather. Given that he cooked for Rasputin, Lenin and Stalin, he is surely the most world-historical chef of modern times. When he was running for president in 2000, Putin proudly revealed the connection but said that his grandfather, a loyal Chekist to the last, had never yielded any secrets of his remarkable career.

Yet Beria, by now Stalin's tireless and hugely competent NKVD boss, super-manager and Politburo grandee, hated the Egnatashvilis because they had closer relations with Stalin than he himself had and because they were Georgians independent of him.

He was determined to destroy them.

Stalin's deadly game

Meanwhile, even though a food taster and catering maestro, Sasha Egnatashvili, whether or not he was Stalin's half-brother, was not immune to the deadly game of Stalin's Byzantine court.

Just before the Second World War, Stalin, whose wife Nadezhda Alliluyeva had committed suicide in 1932, became suspicious about the wives of his henchmen. The pretty young wives of his intimate chef de cabinet, Alexander Poskrebyshev, and of his top military hench-man Marshal Kulik were both shot, but their husbands continued loyally to serve Stalin without complaint. In addition, President Mikhail Kalinin's wife was in prison. And Sasha Egnatashvili's German wife was arrested and shot even as the Rabbit continued to taste the dictator's food.

During the war, Sasha was promoted to general and showered with medals: the rising young Politburo magnate Nikita Khrushchev grumbled in his memoirs that Stalin had made his kebab cook into a bemedalled general. Khrush chev did not know that the so-called cook was in fact Stalin's probable half-brother and trusted NKVD officer. Sasha accom panied Stalin to most of the summit meetings of the war and it was General Egnatashvili who or ganised the Yalta conference for Stalin where he met Franklin D Roosevelt and Winston Chur chill in early 1945.

Vaso Egnatashvili kept his key post in Georgia, but Beria had found a way to break Sasha's position: Stalin hated corruption all his life. While living in many villas and existing in a world of privilege, he was personally uninterested in money and highly austere in his personal arrangements. Yet General Egnatashvili presided over a huge machine of villas and farms and catering systems that produced enormous quantities of food and wine. Most of it went to waste and it seems almost certain that Stalin's chief of security General Vlasik and his senior colleague Egnatashvili were, if not selling this food, enjoying the luxuries at their disposal in wild parties, orgiastic womanising and general decadence.

At least twice, Stalin was presented with evidence of this and forgave Vlasik and Egna tashvili, but eventually Vlasik was dismissed and arrested. Sasha was never arrested. Beria wanted to destroy both brothers, but Stalin protected them. Sasha was left in charge of the Politburo sanatoria in the Crimea, where he died of natural causes in 1948.

On Stalin's death, Beria temporarily became strongman of the Soviet Union and immediately sacked and dismissed Vaso Egnatashvili, who languished in jail until Beria himself was arrested and shot three months later. He died in the Fifties. There are Egnatashvili descendants of Sasha and Vaso in Tbilisi, Moscow and the United States, all displaying the genial charm of their ancestors. Now, finally, the story of Stalin, his possible father Koba Egnatashvili, his putative half-brother the Rabbit, and their connection to President Putin can be revealed.

"Young Stalin" is published by Weidenfeld & Nicolson (£25)