Green Day is an American punk rock band formed in 1987, consisting of members Billie Joe Armstrong, Mike Dirnt, and Tre Cool. They are known for their raw and energetic sound, characterized by Armstrong's distinctive vocals and their use of three-chord song structures. Pioneers of the punk revival, Green Day gained widespread acclaim with their 1994 album "Dookie," which became a touchstone for the genre. Their politically charged 2004 rock opera, "American Idiot," further solidified their influence and significance in music history.