Short answers, pulled from the story.
The Screen Actors Guild began as a rebellion by six actors in March 1933. The founders included Berton Churchill, Charles Miller, Grant Mitchell, Ralph Morgan, Alden Gay, and Kenneth Thomson. Ralph Morgan served as the first president and Alan Mowbray personally funded the organization.
The Screen Actors Guild faced its darkest hour during the Red Scare of the late 1940s when the House Committee on Un-American Activities summoned suspected communists. On the 17th of November 1947, the Screen Actors Guild voted to force its officers to take a non-communist pledge. Ronald Reagan, then president of the Screen Actors Guild, testified before the committee but never publicly named names.
The Screen Actors Guild Ethnic Minorities Committee and the Screen Actors Guild Women's Committee were co-founded in 1972. Kathleen Nolan became the first female president in 1975 and organized protests including a 1979 rally. The Guild fought for the rights of stunt performers and secured Disability Health Plans for two stuntmen and a reimbursement for a disabled stuntwoman in 2010.
The first industry-wide strike occurred in March 1960 against the seven major studios. Actors demanded 6% or 7% of the gross earnings of pictures made since 1948 and sold to television, along with a pension and welfare fund. The dispute was resolved when the Writers Guild of America reached a similar agreement.
An actor was eligible to join by meeting criteria in three categories: principal actor in a Screen Actors Guild production, background actor under the three voucher rule, or one-year member of an affiliated union. The three voucher rule allowed background actors to become Screen Actors Guild-eligible after collecting three valid union vouchers for three separate days of work. The Guild also enforced Global Rule One which stated that no member shall work as a performer for any producer who has not executed a basic minimum agreement with the Guild.
The Screen Actors Guild journey came to a close on the 30th of March 2012 when the membership voted to merge with the American Federation of Television and Radio Artists. This decision marked the end of a 79-year history for the Guild which had represented over 100,000 film and television principal and background performers worldwide. The merger created a unified voice for performers combining the strengths of both unions to negotiate better contracts.