Steve Ballmer has often been described as Bill Gates's alter ego. Whereas Mr Gates is softly spoken, Mr Ballmer's voice booms across crowded gatherings. And just as Mr Gates is intensely focused and reserved, so Mr Ballmer cuts a charismatic figure with his shiny bald dome and strapping physique.

The son of a Ford executive, he has travelled a long way since his upbringing in a Detroit suburb. A close friend of Mr Gates from their days at Harvard, Mr Ballmer joined Microsoft five years after it was founded. He has since run its finance, recruiting and sales operations, amassing a fortune that Forbes magazine says makes him the fourth-richest American, mostly from his nearly 5% stake in Microsoft.

Having graduated with a degree in applied mathematics and economics, Mr Ballmer joined Procter & Gamble - considered a tough finishing school. He left the firm to go to Stanford business school, but dropped out to join Microsoft.