Can Abramovich talk the talk?

Roman Abramovich was just another foreign billionaire when he arrived at Chelsea Football Club in the summer of 2003 with his cheque book.

It was a strange acquisition for a socially awkward gentleman who detests public attention. Eight years on, he has topped the Sunday Times Rich List and is among the most familiar names and faces in the country – but still only his closest friends and associates have heard the publicity-shy Siberian oil baron utter a word.

That will change on Monday afternoon when, in front of a packed gallery in London's Commercial Court, he will enter the witness box, take the oath and, in Russian, answer questions for several days in a case that could see him forced to hand nearly half his estimated £8.3bn fortune to his former business partner, Boris Berezovsky – a case which has embroiled a cast of characters from Russian presidents and Arab sheikhs to murdered journalists and spies.

For a man who does not give interviews, and who deploys his former Special Forces security guards to herd away journalists, the questioning may be a troublesome experience, albeit one which promises to shed light on the world of an unlikely oligarch. (When Mr Berezovsky was busy making his first billion from second-hand cars, Mr Abramovich was selling cigarettes and perfume to his army conscript pals, and running a company making plastic ducks.) His appearance will be the most "box office" moment in a case that already appears the product of a Hollywood writer's pen. It took a skirmish between the two men's security details in a West London boutique in 2007 for the writ to be served. Mr Abramovich has since twice tried to strike out the court action and, even after failing, had not expected that he would be made to testify in open court.

Almost every day for the past four weeks, the Chelsea owner has sat amid banks of lawyers, his headphones plugged in, listening to a Russian translator, characteristically expressionless and unshaven, as his barrister Jonathan Sumption QC has sought to expose holes in the story told by Mr Berezovsky. The 65-year-old one-time Kremlin power-broker claims that Mr Abramovich, whom he once regarded as as a son, intimidated him into handing over commodities interests at a fraction of their worth. Mr Berezovsky is seeking damages of more than $6bn (£3.5bn) for breach of trust, breach of contract and breach of fiduciary duty.

The two men have consistently accused each other of lying over how they carved out for themselves a great stake in the wealth of post-Communist Russia. Now it is the turn of Mr Abramovich's version to bear scrutiny.

Mr Berezovsky's lawyer, Laurence Rabinowitz QC, will tell the court that Mr Abramovich has lied about the commodities deals that made him billions at Mr Berezovsky's expense, and has lied about threatening Mr Berezovsky, with the Kremlin's backing.

At the heart of the matter is a $1.3bn (£800m) payment by Mr Abramovich to Mr Berezovsky in 2001. Mr Abramovich maintains the payment was for krysha, the Russian for roof, meaning protection, either political or in the gangland sense, and represented his "debt of honour" to Mr Berezovsky, without whose influence over Boris Yeltsin's Kremlin, Mr Abramovich admits he would never have got his hands on the oil firm Sibneft, which he sold back to the Russian state in 2005 for $13bn (£8bn).

Mr Berezovsky claims the two were partners, but the agreement could not be written down owing to Mr Berezovsky's political prominence and ambitions. When he fell out with President Putin in 2000 and fled Russia, Mr Abramovich came to him, threatening the continued imprisonment of his close friend Nikolai Glushkov and the reappropriation of his interests by the Kremlin unless he sold them to Mr Abramovich for a much reduced price.

Mr Berezovsky's lawyers will argue: would their client really have delivered such wealth into Mr Abramovich's hands, in return only for a vague agreement that he would make him regular payments over the ensuing years?

And if the $1.3bn payment represented no more than a thank you, and an insurance premium should Mr Berezovsky subsequently regain political influence, why would the two have fallen out so bitterly? If the payment was instead for krysha why would he have paid such a large amount?

Both men's accounts have been revised during the case. Mr Berezovsky's long-term partner,Yelena Gorbunova, told the court of "strange metamorphoses" in the stamps in Mr Abramovich's passport, while they tried to establish who was where and when. Mr Berezovsky, likewise, has been told by Mr Sumption: "Your story is nonsense. You made it up and have simply been found out."

Mr Berezovsky has also been forced to admit that several of his witnesses have been promised shares of any recoveries he makes from the action. It has added to speculation that the one-time second-richest man in Russia might not have much of his fortune left. It had been alleged that he paid $50m to an unknown party for a secret tape recording of a crucial meeting he had with his former business partner Badri Patarkatsishvilli and Mr Abramovich. He said he had "swapped it for my boat, Thunder B", to the incredulity of the court.

It is unlikely, if not impossible, that the precise truth of what has gone on between the two men will come to light in this court case, but as Mr Abramovich is only too aware, it is upon Mr Berezovsky's shoulders, as the claimant, to prove the truth of his version of events. If he does so, he will be a very rich man – again. And Mr Abramovich? Well, he'll still be a very rich man.

Roman vs Boris: The Supporting Cast

Yelena Gorbunova

Berezovsky's long-term partner, He only recently divorced his wife, at a cost of £100m.

Dasha Zhukova

Abramovich's partner. The daughter of a Russian oil magnate and arms dealer.

Boris Yeltsin

Berezovsky convinced him to sell state assets in return for support from his TV network.

Vladimir Putin

Fell out with Berezovsky, who fled Russia. Backing Berezovsky against Abramovich.

Sheikh Sultan

Crown Prince of Abu Dhabi acted as an intermediary in transfer of $1.3bn between the men.

Stephen Curtis

Lawyer to the oligarchs, helped them hide funds. Died in a helicopter crash in 2004.

Paul Klebnikov

Journalist. Subject of 2001 libel action by Berezovsky. Shot dead in Moscow in 2004.

Badri Patarkatsishvilli

Berezovsky's business partner. In 2008, died of a heart attack at his Surrey mansion.

Oleg Deripaska

Russian aluminium magnate alleged to have conspired with Abramovich against Berezovsky.

Mikhail Chernoy

Israeli aluminium magnate, subject of international arrest warrant, refused to testify.

Andrei Lugovoi

Patarkatsishvilli's former security chief. Made secret tape of meeting bought by Berezovsky for $50m.

Alexander Litvinenko

Probed attempt to kill Berezovsky. Poisoned in 2006. Lugovoi is main suspect.