Kweku Adoboli, the ex-UBS trader accused of losing the Swiss bank $2.3 billion, was a "star" and his desk was doing "amazingly well" in the months before the debacle, a London court heard on Thursday.
However, Christophe Bertrand, the most junior of the four traders who made up the Exchange Traded Funds (ETFs) desk where Adoboli worked, also said the alleged "rogue trader" could be unfriendly and difficult to work with.
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Adoboli, 32, was arrested in September 2011, and is on trial at Southwark Crown Court accused of fraud and false accounting, charges he denies.
Bertrand told the court Adoboli and the other senior trader on the ETFs desk, John Hughes, conducted most of the proprietary trading done on the desk and 2011 had started well for them.
He said that as far as he was aware, the desk had made about $70 million in profits in the first half of the year, mostly from proprietary trading, compared with about $15 to $20 million for the whole of the previous year.
"It (the desk) was doing amazingly well," he said. "Other senior traders would come to our desk to ask us for our advice. Everyone knew it was Kweku Adoboli and John Hughes doing the proprietary trading. They were the stars of the trading floor."
The prosecution has presented Adoboli as a "master fraudster" who routinely exceeded risk limits and masked his positions with fictitious hedging trades.
The defense has portrayed him as a hard-working team player who believed his trading and accounting methods were for the good of the bank and of his colleagues.
Bertrand said Adoboli had mentioned to him at least once in 2011 his "umbrella". This, according to the prosecution, was a secret fund Adoboli used to park profits from unauthorized trades and leak them into the official accounts to plug losses.
But Bertrand said he did not have a full understanding of what the umbrella was and that as a junior team-member focused on client trading he did not delve into the matter in any depth.
Bertrand gave an unflattering description of Adoboli, who was in charge of training him when he joined the ETFs desk in June 2010.
"He was quite rough. One of the rules he had put in place was that I could not ask the same question twice. Quite often when I asked a question he gave me the silent treatment," Bertrand said.
Bertrand, who is French, was asked by the judge whether he could find a better word than "rough" to describe Adoboli's attitude to him. "Unfriendly, unpleasant, superior," he replied.
Bertrand's evidence was in sharp contrast to what the jury had heard from previous witnesses, and from excerpts from Adoboli's performance appraisals, in which he came across as a friendly, approachable team player.
Evidence read out in court revealed that Bertrand's fellow traders had given him two nicknames.
One was "Bateman", in reference to a perceived physical resemblance with the main character in the film "American Psycho". The other was "FFF", an acronym for something rude. The jury were advised not to speculate on what it might mean.