|James K. Polk: Speaker of the House AND President of United States|
Only one former Speaker of the House was ever elected President of the United States. That was James K. Polk. He was Speaker from 1835-1839 and President from 1845-1849.
Henry Clay came close. He was Speaker from 1811-1821 and again from 1823-1825. He was a serious contender for the presidency in 1824, 1832, and 1844.
The presidential election of 1844 pitted two former Speakers: Polk and Clay.
Something for Paul Ryan to think about.