Debs was a popular American socialist around the turn of the 20th century, emerging as an organizer of railroad workers.
Debs was a leader of many failed actions in the late 1800s, most notably the American Railway Union's sympathy boycott in support of the Pullman Strike, for his role in which he was imprisoned for 6 months. He mostly spent these months reading about socialism, and was convinced.
Debs was one of the founders of the Socialist Party of America, formed in 1901. He ran for president of the USA five times, with his best result being 6% of the popular vote in 1912.
In 1918, Debs was sentenced to 10 years in prison for a speech denouncing American participation in World War I. He developed health problems in prison and though his sentence was commuted in 1921, he died soon afterward.