Who was the first president to be speaker of the house?

No US President has gone on to become Speaker after their presidency. The closest thing to that was when former President Taft was made the Chief Justice of the US Supreme Court in 1921.

The only Speaker of the House to become President was James K. Polk. President Gerald Ford, when nominated to become Vice President in 1973, was serving as the House Minority Leader. Lyndon Johnson, when elected Vice President, was the Senate Majority Leader.