John Llewellyn Lewis (February 12, 1880 June 11, 1969) was an American leader of organized labor who served as president of the United Mine Workers of America (UMW) from 1920 to 1960. A major player in the history of coal mining, he was the driving force behind the founding of the Congress of Industrial Organizations (CIO), which established the United Steel Workers of America and helped organize millions of other industrial workers in the 1930s, during the Great Depression. After resigning as head of the CIO in 1941, Lewis took the United Mine Workers out of the CIO in 1942 and in 1944 took the union into the American Federation of Labor (AFL).

Lewis was a Republican, but he played a major role in helping Democrat Franklin D. Roosevelt win a landslide victory for the US Presidency in 1936. He was an isolationist, and broke with Roosevelt in 1940 on FDR's anti-Nazi foreign policy. Lewis was an effective, aggressive fighter and strike leader who gained high wages for his membership while steamrolling over his opponents, including the United States government. Lewis was one of the most controversial and innovative leaders in the history of labor, gaining credit for building the industrial unions of the CIO into a political and economic powerhouse to rival the AFL. But during World War II, he was widely criticized by calling nationwide coal strikes, which critics believed to be damaging to the American economy and war effort.

His massive leonine head, forest-like eyebrows, firmly set jaw, powerful voice, and ever-present scowl thrilled his supporters, angered his enemies, and delighted cartoonists. Coal miners for 40 years hailed him as their leader, whom they credited with bringing high wages, pensions and medical benefits. After his successor died shortly after taking office, Lewis hand-picked Tony Boyle, a miner from Montana, to take the presidency of the union in 1963.

A trade union (labor union in American English), often simply referred to as a union, is an organization of workers who have come together to achieve common goals, such as protecting the integrity of their trade, improving safety standards, and attaining better wages, benefits (such as vacation, health care, and retirement), and working conditions through the increased bargaining power wielded by solidarity among workers. Trade unions typically fund the formal organization, head office, and legal team functions of the trade union through regular fees or union dues. The delegate staff of the trade union representation in the workforce are made up of workplace volunteers who are appointed by members in democratic elections.

The trade union, through an elected leadership and bargaining committee, bargains with the employer on behalf of union members (rank and file members) and negotiates labour contracts (collective bargaining) with employers. The most common purpose of these associations or unions is "maintaining or improving the conditions of their employment". This may include the negotiation of wages, work rules, occupational health and safety standards, complaint procedures, rules governing status of employees including promotions, just cause conditions for termination, and employment benefits.

Unions may organize a particular section of skilled workers (craft unionism), a cross-section of workers from various trades (general unionism), or attempt to organize all workers within a particular industry (industrial unionism). The agreements negotiated by a union are binding on the rank and file members and the employer and in some cases on other non-member workers. Trade unions traditionally have a constitution which details the governance of their bargaining unit and also have governance at various levels of government depending on the industry that binds them legally to their negotiations and functioning.

Originating in Great Britain, trade unions became popular in many countries during the Industrial Revolution. Trade unions may be composed of individual workers, professionals, past workers, students, apprentices or the unemployed. Trade union density, or the percentage of workers belonging to a trade union, is highest in the Nordic countries.