Mayor of Philadelphia from 1828 to 1829 who was the eleventh Vice President of the United States from 1845 to 1849, under President James K. Polk. He was also a US Senator from Pennsylvania from 1831 to 1833.
Elected on the same ticket as Polk, he acted in the Senate to cast the tie-breaking vote to overturn a protective tariff.
The county of Dallas, in Texas - as well as Dallas counties in Iowa and Missouri - were named after him.
His father Alexander Dallas was Secretary of the Treasury under President James Madison.
He had a longtime rivalry with James Buchanan, from his days in Philadelphia government to the administration of James K. Polk.