Judge Richard Posner has been described by his peers as one of the most important anti-trust scholars in the last half century.

His standing among anti-trust scholars made him a logical choice to serve as mediator for settlement talks between the government and Microsoft.

Judge Thomas Penfield Jackson, who was overseeing the case, has repeatedly encouraged both sides to come to some kind of agreement.

However, they remained far apart even after Judge Jackson issued a withering preliminary ruling which found Microsoft had abused its monopoly power and harmed consumers.

With little to show after three face-to-face meetings, the judge asked Mr Posner to act as mediator.

Prolific writer and thinker

Judge Posner is a leading scholar on how economics and the law interact, applying the free market theories of the Chicago School and Milton Friedman.

He has applied cost-benefit and efficiency analysis to a wide range of legal issues, and has written more than 30 books and numerous articles in legal journals and the press.

Unlike many on the bench, Judge Posner has waded fearlessly into some of the most contentious areas of public debate, including sexuality, adoption, rape, Aids and human cloning.

Many believe that his outspoken work has been the only thing which has stood in the way of his appointment to the US Supreme Court. But as Ian Ayres of the Yale Law School once wrote, Judge Posner is "a man driven by an intellectual vision, not by concerns with promotion".

In a famous 1978 article, he argued that buying and selling babies on the open market would encourage adoption.

Demand for newborns constantly outstripped supply because there was no pricing mechanism, he said.

Anti-trust expert

A significant amount of his writings deals with anti-trust law, an area where his two interests - law and economics - meet.

Before being appointed to the federal court in 1981 by President Ronald Reagan, he helped found Lexecon Incorporated, a consultancy which advanced the economic theories of the Chicago School.

The consultancy counted among its early clients several companies which wanted to know if their business practices violated anti-trust law.

And early in his career in the mid-1970s, he wrote two books on anti-trust case history and law.

He called for major reforms in the application of anti-trust law, arguing for a narrow view of anti-trust law that would regulate only the most obvious and egregious examples of price-fixing by corporate coalitions and mergers that would eliminate competition.

However, his writings and rulings do not shed much light on how he might view the Microsoft case.

Unlike the cartels and corporate coalitions he addressed in his books on anti-trust law, Microsoft is a single company which gained a dominant market position.

The fact that his position was unclear only bolstered his standing as a mediator.