As Vladimir Putin nears his 70th birthday on Friday, how did he become the isolated autocrat who launched his disastrous invasion of Ukraine?

Seven pivotal moments in his life helped shape his thinking and explain his growing estrangement with the West.

Born in a Leningrad still scarred by its 872-day siege in World War Two, young Vladimir was a surly and combative boy at school – his best friend recalled that “he could get into a fight with anyone” because “he had no fear”.

Nonetheless, a slight but scrappy young boy in a city overrun with street gangs needed an edge, and at the age of 12 he took up first sambo, a Russian martial art, and then judo. He was determined and disciplined, and by the time he was 18 had a judo black belt and third place in the national junior competition.

Of course, this has since been used as part of his carefully-curated macho persona, but it also confirmed his early belief that in a dangerous world, you need to be confident but also realise that, in his own words, when a fight is inevitable, “you must hit first, and hit so hard that your opponent will not rise to his feet”.

On the whole, people avoided going to 4 Liteyny Prospekt, the KGB political police HQ in Leningrad. So many had passed through its interrogation cells to the gulag labour camps in the Stalin era that the bitter joke was that the so-called Bolshoi Dom, the “Big House”, was the tallest building in Leningrad, because one could see Siberia from its basement.

Nonetheless, when he was 16, Putin entered its red-carpeted reception and asked the rather bemused officer behind the desk how he could join. He was told that he needed to have completed military service or a degree, and so he even asked which degree was best.

Law, he was told – and from that point, Putin was determined to graduate in law, after which he was duly recruited. To Putin the street-smart bruiser, the KGB was the biggest gang in town, offering security and advancement even to someone with no Party connections.

But it also represented a chance to be a mover and shaker – as he himself said about the spy films he watched as a teenager, “one spy could decide the fate of thousands of people”.

For all his hopes, Putin’s KGB career never really took off. He was a solid worker, but no high flier. Nonetheless, he had applied himself to learning German, and this got him an appointment to the KGB’s liaison offices in Dresden in 1985.

There he settled into a comfortable expat life, but in November 1989, the East German regime began to collapse, with shocking speed.

On 5 December, a mob surrounded the Dresden KGB building. Putin desperately rang the nearest Red Army garrison to request protection, and they helplessly replied “we cannot do anything without orders from Moscow. And Moscow is silent.”

Putin learned to fear the sudden collapse of central power – and determined never to repeat what he felt was Soviet leader Mikhail Gorbachev’s mistake, not to respond with speed and determination when faced by opposition.

Putin would later leave the KGB as the Soviet Union imploded, but soon secured a position as fixer for the reformist new mayor of what was now St Petersburg.

The economy was in freefall, and Putin was charged with managing a deal to try and help the city’s people get by, swapping $100m (£88m) worth of oil and metal for food.

In practice, no one saw any food, but according to an investigation, quickly suppressed, Putin, his friends and the city’s gangsters pocketed the money.

In the “wild 90s”, Putin quickly learned that political influence was a monetisable commodity, and gangsters could make useful allies. When everyone around him was profiting from their positions, why shouldn’t he?

When Putin became Russian president in 2000, he hoped to be able to build a positive relationship with the West – on his own terms, including a sphere of influence across the former Soviet Union. He soon became disappointed, then angry, believing the West was actively trying to isolate and demean Russia.

When Georgian president Mikheil Saakashvili committed his country to joining Nato, Putin saw red and a Georgian attempt to regain control over the Russian-backed breakaway region of South Ossetia became an excuse for a punitive operation.

In five days, Russian forces shattered the Georgian military and forced a humiliating peace on Saakashvili.

The West was outraged, yet within a year, US president Barack Obama was offering to “reset” relations with Russia, and Moscow was even awarded the right to host the 2018 football World Cup.

To Putin, it was clear that might made right – and a weak and inconstant West would huff and puff, but ultimately back down in the face of a determined will.

A widespread – and credible – belief that the 2011 parliamentary elections were rigged sparked protests that were only galvanised when Putin announced that he would be standing for re-election in 2012.

Known as the “Bolotnaya Protests” after the Moscow square that they filled, this represented the largest expression of public opposition yet under Putin.

His belief was that the rallies were initiated, encouraged and directed by Washington, blaming US Secretary of State Hillary Clinton personally.

To Putin, it was evidence that the gloves were off, and the West was coming directly for him, and that, in effect, he was now at war.

When Covid-19 swept across the globe, Putin went into an isolation unusual even for personalistic autocrats, with anyone going to meet him being isolated for a fortnight under guard and then having to pass through a corridor bathed in germ-killing ultraviolet light and fogged in disinfectant.

In this time, the number of allies and advisers able to have face time with Putin shrank dramatically to a handful of yes-men and fellow hawks.

Exposed to fewer alternative opinions and scarcely even seeing his own country, Putin seems to have “learned” that all his assumptions were right and all his prejudices justified, and the seeds of the invasion of Ukraine were planted.

Professor Mark Galeotti is an academic and author, whose books include We Need To Talk About Putin and the forthcoming Putin’s Wars