A High Court judge described Chelsea Football Club owner Roman Abramovich today as "courteous", "careful", "thoughtful" and "frank".
But Mrs Justice Gloster said she had "little doubt" that the Russian billionaire could be a "ruthless" businessman.
The judge was analysing Mr Abramovich's evidence during a multibillion-pound High Court battle with Russian oligarch Boris Berezovsky.
Mrs Justice Gloster ruled in Mr Abramovich's favour when delivering a summary judgment last month.
Today, she published a full ruling, in which her thoughts were outlined in more detail.
Mr Berezovsky claimed more than £3 billion damages after accusing Mr Abramovich of blackmail, breach of trust and breach of contract.
Mr Abramovich denied the allegations and denied that Mr Berezovsky was entitled to damages.
Mrs Justice Gloster dismissed Mr Berezovsky's claims last month after a trial in London which started in October 2011 and ended in January.
Mrs Justice Gloster said Mr Abramovich had given evidence in Russian and his answers were translated into English.
She said he had been cross-examined over nine days by a barrister representing Mr Berezovsky.
"It was obvious that his ability to speak, understand or read English was limited and I had no reservations about the genuine nature of his wish to give his evidence in Russian," said the judge in her full ruling.
"I did not form the impression that Mr Abramovich in any way used the translation process as a means of evading giving a direct answer or of delaying his answers to any questions put to him.
"Despite the fact that he gave his evidence in Russian, I was able to form a clear view of his demeanour and credibility from the answers which he gave and the manner in which he gave them."
She added: "He was also unfailingly courteous to the court and counsel who were cross-examining him."
The judge said cross-examination was a "very revealing" process.
"However well-prepared a witness may be, or however controlled he may appear to be when giving his answers, it is very rare that the court is not able to reach a conclusion as to whether he is telling the truth or not," she said.
Court artist sketch by Elizabeth Cook of Russian oligarch Boris Berezovsky
"Contrary to Mr Berezovsky's views, Mr Abramovich did not present himself in cross-examination as a 'humble man' or as someone who was attempting to appear likeable, or to be liked.
"Whilst his demeanour was reserved and restrained, he made no attempt to pretend that he was anything other than a highly successful and very wealthy businessman, who had made a very substantial fortune in the challenging Russian business environment of the 1990s and early 2000s, largely as a result of his and his colleagues' entrepreneurial, management and financial skills."
She added: "I also had little doubt that, if the need arose, he would have been prepared to act ruthlessly in a business context to achieve his commercial goals."
Mrs Justice Gloster said Mr Abramovich had been "focussed".
"Mr Abramovich indeed gave careful and thoughtful answers, which were focused on the specific issues about which he was being questioned," said the judge.
"At all times, he was concerned to ensure that he understood the precise question, and the precise premise underlying the question which he was being asked.
"He was meticulous in making sure that, despite the difficulties of the translation process, he understood the sense of the questions which were being put to him."
She added: "It ... reflected Mr Abramovich's responsible approach to giving answers which he could honestly support.
"Where he had relevant knowledge, he was able to give full and detailed answers; he took care to distinguish between his own knowledge, reconstructed assumptions and speculation.
"He was not afraid to give answers which a less scrupulous witness would have considered unhelpful to his case."
The judge went on: "I found Mr Abramovich to be frank in making concessions where they were due, for example in relation to the backdating of documents, the concealment of his 44% beneficial interest in (oil firm) Sibneft, or in relation to the mis-description of his educational qualifications in a Sibneft circular (the last of which I suspect largely arose as a result of translation difficulties and which were, in any event, of minimal importance)."
She concluded that Mr Abramovich was a "truthful" and "on the whole reliable" witness.
The judge found Mr Berezovsky to be 'unimpressive'
Mrs Justice Gloster formed a different view of Mr Berezovsky.
"On my analysis of the entirety of the evidence, I found Mr Berezovsky an unimpressive, and inherently unreliable, witness, who regarded truth as a transitory, flexible concept, which could be moulded to suit his current purposes," said the judge.
"At times, the evidence which he gave was deliberately dishonest; sometimes he was clearly making his evidence up as he went along in response to the perceived difficulty in answering the questions in a manner consistent with his case; at other times, I gained the impression that he was not necessarily being deliberately dishonest, but had deluded himself into believing his own version of events.