Bill Gates is preparing to take the stand at a hearing into Microsoft's anti-trust settlement with the US government.
He will lead the company's attempts to forestall harsh penalties proposed by the nine states that have rejected the deal. Mr Gates is scheduled to appear after Mr David Cole, a senior vice-president of Microsoft Network.
The states want a modular version of Windows that's capable of readily incorporating third-party features. They also want the court to force Microsoft to divulge blueprints for its Internet Explorer browser.
Commentators believe Mr Gates could be the best person to persuade Judge Colleen Kollar-Kotelly the proposals would hurt consumers.
Mr Andy Gavil, a Howard University law professor, said: "In a sense, he is the shadow defendant. Microsoft is his alter ego. If they want to make a credible case that these remedies would be damaging, he's got to make that case".
Lawyers for the states say Mr Gates's questioning could take about two days.