Thomas Swann was an American lawyer and politician who also was President of the Baltimore and Ohio Railroad as it completed track to Wheeling and gained access to the Ohio River Valley. Initially a Know-Nothing, and later a Democrat, Swann served as the 19th Mayor of Baltimore (1856–1860), later as the 33rd Governor of Maryland (1866–1869), and subsequently as U.S. Representative ("Congressman") from Maryland's 3rd congressional district and then 4th congressional district (1869–1879), representing the Baltimore area.

The Know Nothings were a nativist political movement in the United States in the 1850s, officially known as the Native American Party before 1855, and afterwards simply the American Party. Members of the movement were required to say "I know nothing" whenever they were asked about its specifics by outsiders, providing the group with its colloquial name.