(1767–1848), 6th president of the US 1825–29; a Massachusetts Democratic-Republican; eldest son of President John Adams. His ministerial positions from 1794 to 1801 included appointments to the Netherlands, Portugal, and Prussia. After serving in the US Senate 1803–08, he was minister to Russia, then to England. He helped negotiate the Treaty of Ghent 1814, which ended the War of 1812. As President Monroe's secretary of state 1817–25, he was the chief architect of the Monroe Doctrine. His impassioned advocacy of the abolition of slavery and the safeguarding of freedom of speech defined his postpresidential career as a member of the US House of Representatives 1831–48.