William Dudley "Big Bill" Haywood (February 4, 1869 – May 18, 1928) was an American labor organizer and founding member and leader of the Industrial Workers of the World (IWW) and a member of the executive committee of the Socialist Party of America. During the first two decades of the 20th century, Haywood was involved in several important labor battles, including the Colorado Labor Wars, the Lawrence Textile Strike, and other textile strikes in Massachusetts and New Jersey.

Haywood was an advocate of industrial unionism, a labor philosophy that favors organizing all workers in an industry under one union, regardless of the specific trade or skill level; this was in contrast to the craft unions that were prevalent at the time, such as the AFL. He believed that workers of all ethnicities should be united, and favored direct action over political action.

Haywood was often targeted by prosecutors due to his support for violence. An attempt to prosecute him in 1907 for his alleged involvement in the murder of Frank Steunenberg failed, but in 1918 he was one of 101 IWW members jailed for anti-war activity during the First Red Scare. He was sentenced to twenty years. In 1921, while out of prison during an appeal of his conviction, Haywood fled to the Soviet Union, where he spent the remaining years of his life.