"To be honest, I've only ever met him the once but he gave the impression of having a brain the size of a planet, says one Omnicom agency chief executive, who is impressed with Weisenburger's intellect but seems unsure of his social skills. And both BBDO's head of Europe, Michael Baulk, and DDB's UK group chairman, James Best, claim to have only encountered their respective agencies' chief paymaster on just the odd occasion.
Equally, Weisenburger's peers within the financial departments at rival agency networks were either unable or unwilling to discuss their opposite number and, given the current unfriendly fire directed at Omnicom, it's perhaps not surprising that the man himself is keeping his head down.
However, a preliminary delve into Weisenburger's past does uncover some revealing hints of the character behind Omnicom's financial reporting - Weisenburger seems to come very much from the mould of Omnicom's chief executive, John Wren, who was responsible for initially appointing him.
The legend goes that the pair first met at their daughters' primary school in Greenwich, Connecticut - the hometown of the majority of New York's advertising aristocracy. Wren was looking for a successor to replace Omnicom's long-standing and highly regarded chief financial officer, Fred Meyer, who was due to retire. He coyly asked Weisenburger, who was a founding member, president and chief executive officer of the New York investment bank Wasserstein Perella (which he had run for more than a decade), if he knew of any suitable candidates as a covert way of offering him the job.
The story goes that Weisenburger did not realise what Wren was driving at, and politely supplied a list of candidates he thought suitable. When Wren became less subtle in displaying his intentions the penny finally dropped and Weisenburger was faced with a difficult choice. After all, he had spent the majority of his career wheeling and dealing on the mergers and acquisitions circuit rather than working within a corporation of the scale of Omnicom.
Weisenburger, 43, gained his reputation and a certain amount of notoriety for having graduated top of his MBA class at the University of Pennsylvania's Wharton School of Business in 1987. He also obtained a BS degree in Finance and Accounting from Virginia Tech - further evidence of his intellectual credentials. Before Wasserstein Perella, he worked at Coopers & Lybrand and First Boston Corp.
His city career had given Weisenburger a reputation for identifying and carrying out astute acquisitions and mergers. He orchestrated the sale of Maybelline to L'Oreal in 1996 and it was this sort of shrewd buyout experience that Wren, himself still relatively new in the job, wanted within Omnicom to replace the out-going Meyer.
The grand plan was that Wren and Weisenburger would make up the young blood to succeed the existing chief executive officer, Bruce Crawford, and Meyer, both of whom were then past pensionable age.
Wren, with his own image as a dealmaker and smart financier, was keen to change the pace at which Omnicom advanced.
However, Weisenburger's time at Wasserstein Perella had produced one blot on his copybook by the time that he took up his position at Omnicom. It came with the final acquisition to which his name was linked at the merchant bank - that of the stricken cosmetics company Yardley. The purchase went badly wrong and Yardley ended up in receivership.
Nonetheless, despite any doubts Weisenburger had, he accepted the job and his three years at Omnicom, alongside the triumvirate of Wren and the company's secretary and general counsel, Barry Wagner, have been marked by aggressive growth accompanied by indisputably clever accounting.
Ironically, of course, it's this skill with the books that led to the critical Wall Street Journal article of 12 June and the subsequent threats of the credit insurer Euler TI to withdraw its cover of Omnicom's dealings.
The ongoing controversy has thrust Wren and Weisenburger into the spotlight.
And the man behind the seemingly impenetrable Weisenburger mask? "He works incredibly hard, takes his job very seriously, he's got a good reputation with the investor community but he's good fun to be with," Omnicom vice-chairman, Peter Mead, testifies.
Certainly, for a man employed on the beancounting side of the business, Weisenburger defies stereotypes. He lives an exceptionally active life outside of Omnicom and, despite his rather dour image, spends much of his leisure time climbing mountains and running marathons.
Inside work it seems to be a very different matter - Omnicom's Madison Avenue headquarters is not known for being decked out in a flamboyant or extravagant way, and this refusal to put on a conspicuous display of wealth extends to the financial reporting.
Compared with WPP's impressive and fancy annual reports, Omnicom's financial documents have all the charm of a University final year exam paper. This seems very much to mirror the business-like but clever attitude of Weisenburger himself.