Leon Frank Czolgosz (/ˈtʃaʊɡɔːʃ/ CHOW-gawsh) was an American steelworker and anarchist known for the assassination of President William McKinley.

Czolgosz believed there was a great injustice in American society, an inequality which allowed the wealthy to enrich themselves by exploiting the poor. He concluded that the reason for this was the structure of government.

About this time, Leon learned of the assassination of a leader in Europe, King Umberto I of Italy, who had been shot dead by anarchist Gaetano Bresci on July 29, 1900. Bresci told the press that he had decided to take matters into his own hands for the sake of the common man.

On September 6, Czolgosz went to the Pan-American Exposition where McKinley was speaking. Leon was armed with a concealed .32 caliber Iver Johnson "Safety Automatic" revolver he had purchased four days earlier. He approached McKinley, who had been standing in a receiving line inside the Temple of Music, greeting the public for ten minutes.

At 16:07, Czolgosz reached the front of the line. When McKinley extended his hand, Czolgosz slapped it aside and shot the President twice in the abdomen at point blank range: the first bullet ricocheted off a coat button and lodged in McKinley's jacket; the other seriously wounded him in the stomach.

The president died on September 14 after his wound became infected. Caught in the act, Czolgosz was quickly tried, convicted, and executed by the State of New York seven weeks later on October 29, 1901.

In the hours before his execution, he refused to repent to two different groups of priests. The final group of priests pleaded for 45 minutes for him to repent, but he refused and they left.

Following McKinley's assassination, Theodore Roosevelt was inaugurated and began a series of wide sweeping capitalist reforms including trust busting and nationalizing public lands.