Chelsea Football Club owner Roman Abramovich is a genius, a Russian oligarch has told a High Court judge.
Boris Berezovsky, 65, was giving evidence as part of his bid to win £3bn in damages from Mr Abramovich for an alleged breach of trust and contract.
The Commercial Court has heard that Berezovsky alleges that his former business partner "intimidated" him into selling shares in Russian oil firm Sibneft for a fraction of their value.
Mr Abramovich, 44, denies the claims.
On the fifth day of a trial, Mr Berezovsky, said: "(Mr Abramovich) is genius, at least in one way.
"If he wants to convince somebody personally he may serve them so well. And you trust him so much that you really believe he is sincere.
"He is genius.
"He really convinced me for a long time he is like my son... He is genius like that, no doubt."
Mr Berezovsky, also described media mogul Rupert Murdoch, who he said he had established a radio company with, as a "great businessman".
Jonathan Sumption QC, for Mr Abramovich, said Mr Berezovsky had told the court that Mr Abramovich was "not smart".
Mr Berezovsky, who has lived in exile in the UK since 2001, replied: "It's not so."
'Good at psychology'
On Thursday, Mr Berezovsky told court Mr Abramovich was "good at getting people to like him and good at psychology in that way".
"He is good at appearing to be humble," he told the judge, Mrs Justice Gloster.
"He is happy to spend days just socialising with important or powerful people if that is what is needed so he can get closer to them."
The trial is expected to last more than two months.