The golden age is popularly considered to have begun in 1938 with the debut of Superman in Action Comics #1, published by DC Comics. Superman was so popular that superheroes soon dominated the pages of comic books.
The golden age arguably ended in 1951 when the title All-Star Comics ceased to chronicle the adventures of the superhero team the Justice Society of America and changed its name with #58 to All-Star Western. This marked the decline of superheroes in the medium and the 1950s marked a major slump in comics popularity.
See also: Silver Age of Comic Books