In the US, by the late 1930s and early 1940s, swing music had become the most popular musical style and remained so for several years, until it was supplanted in the late 1940s by the pop standards sung by the crooners who grew out of the big band Swing Era tradition. Bandleaders such as the Dorsey Brothers often helped launch the careers of vocalists who went on to popularity as solo artists, such as Frank Sinatra, whom rose to fame as a singer during this time. Sinatra's vast appeal to the "Bobby soxers" revealed a whole new audience for popular music, which had generally appealed mainly to adults up to that time, making Sinatra the first teen idol.