He invested $150M in Apple in '97. Insiders said that Apple was days away from shutting down completely when he did that. Microsoft was already fighting anti-trust suits and didn't need their one competitor to close shop; that would have made them a complete monopoly over the personal computer OS market. So, they stuck a deal: Apple drops their lawsuits against M$, make IE the default standard browser for MacOS, and re-install Steve Jobs as CEO and in return Microsoft will continue to develop MS Office for the Mac and other software... oh, and here's $150M to keep you afloat.