A new High Court case between oligarchs from the former Soviet Union opened in London on Monday, and is expected to go on into next year.
Israel-based Michael Cherney wants a judge to uphold his claim that he is a partner in an aluminium business with Russian tycoon Oleg Deripaska.
But Mr Deripaska denies that there was a commercial arrangement between the two men and instead says that the $250 million he previously paid to Mr Cherney was protection money extorted from him.
Mr Cherney, who grew up in Uzbekhistan, will give his evidence by video from Tel Aviv. He is wanted by Spain over allegations about money-laundering and organised crime according to an Interpol warrant issued three years ago, but has remained in Israel.
Judgment is still awaited in another high-profile High Court oligarchs case, between Boris Berezovsky and Roman Abramovich, which ended six months ago.