Henry Louis Mencken (September 12, 1880 – January 29, 1956) was an American journalist, essayist, satirist, cultural critic, and scholar of American English. He commented widely on the social scene, literature, music, prominent politicians, and contemporary movements. His satirical reporting on the Scopes Trial, which he dubbed the "Monkey Trial", also gained him attention. The term "Menckenian" has entered multiple dictionaries to describe anything of or pertaining to Mencken, including his combative rhetorical and prose style.

As a scholar, Mencken is known for The American Language, a multi-volume study of how the English language is spoken in the United States. As an admirer of the German philosopher Friedrich Nietzsche, he was an outspoken opponent of organized religion, theism, and representative democracy, the last of which he viewed as a system in which inferior men dominated their superiors. Mencken was a supporter of scientific progress and was critical of osteopathy and chiropractic. He was also an open critic of economics.

Mencken opposed the American entry into World War I and World War II. Some of the opinions in his private diary entries have been described by some researchers as racist and anti-Semitic, although this characterization has been disputed. Larry S. Gibson argued that Mencken's views on race changed significantly between his early and later writings, and that it was more accurate to describe Mencken as elitist rather than racist. He seemed to show a genuine enthusiasm for militarism but never in its American form. "War is a good thing," he wrote, "because it is honest; it admits the central fact of human nature.... A nation too long at peace becomes a sort of gigantic old maid."

His longtime home in the Union Square neighborhood of West Baltimore was turned into a city museum, the H. L. Mencken House. His papers were distributed among various city and university libraries, with the largest collection held in the Mencken Room at the central branch of Baltimore's Enoch Pratt Free Library.