William Jennings Bryan (March 19, 1860 – July 26, 1925) was an American lawyer, orator and politician. Beginning in 1896, he emerged as a dominant force in the Democratic Party, running three times as the party's nominee for President of the United States in the 1896, 1900, and 1908 elections. He served in the House of Representatives from 1891 to 1895 and as the Secretary of State under Woodrow Wilson from 1913 to 1915. Because of his faith in the wisdom of the common people, Bryan was often called "The Great Commoner", and because of his rhetorical power and early fame as the youngest presidential candidate, "The Boy Orator".

Born and raised in Illinois, Bryan moved to Nebraska in the 1880s. He won election to the U.S. House of Representatives in the 1890 elections, served two terms, and made an unsuccessful run for the U.S. Senate in 1894. At the 1896 Democratic National Convention, Bryan delivered his "Cross of Gold" speech which attacked the gold standard and the eastern moneyed interests and crusaded for inflationary policies built around the expanded coinage of silver coins. In a repudiation of incumbent President Grover Cleveland and his conservative Bourbon Democrats, the Democratic convention nominated Bryan for president, making Bryan the youngest major party presidential nominee in U.S. history. Subsequently, Bryan was also nominated for president by the left-wing Populist Party, and many Populists would eventually follow Bryan into the Democratic Party. In the intensely-fought 1896 presidential election, the Republican nominee, William McKinley, emerged triumphant. At age 36, Bryan remains the youngest person in United States history to receive an electoral vote for president. Bryan gained fame as an orator, as he invented the national stumping tour when he reached an audience of 5 million people in 27 states in 1896.

Bryan retained control of the Democratic Party and again won the presidential nomination in 1900. After the Spanish–American War, Bryan became a fierce opponent of American imperialism, and much of his campaign centered on that issue. In the election, McKinley again defeated Bryan and won several Western states that Bryan had won in 1896. Bryan's influence in the party weakened after the 1900 election, and the Democrats nominated the conservative Alton B. Parker in the 1904 presidential election. Bryan regained his stature in the party after Parker's resounding defeat by Theodore Roosevelt and voters from both parties increasingly embraced some of the progressive reforms that had long been championed by Bryan. Bryan won his party's nomination in the 1908 presidential election, but he was defeated by Roosevelt's chosen successor, William Howard Taft. Along with Henry Clay, Bryan is one of the two individuals who never won a presidential election despite receiving electoral votes in three separate presidential elections held after the ratification of the Twelfth Amendment.

After the Democrats won the presidency in the 1912 election, Woodrow Wilson rewarded Bryan's support with the important cabinet position of Secretary of State. Bryan helped Wilson pass several progressive reforms through Congress. In 1915, he considered that Wilson was too harsh on Germany and finally resigned after Wilson had sent Germany a note of protest with a veiled threat of war in response to the sinking of the Lusitania by a German U-boat. After leaving office, Bryan retained some of his influence within the Democratic Party, but he increasingly devoted himself to Prohibition, religious matters, and anti-evolution activism. He opposed Darwinism on religious and humanitarian grounds, most famously in the 1925 Scopes Trial, dying soon after. Bryan has elicited mixed reactions from various commentators, but is acknowledged by historians as one of the most influential figures of the Progressive Era.