Billie Joe Armstrong (born February 17, 1972) is an American singer, songwriter, musician, guitarist, multi-instrumentalist, and actor who is best known as the lead vocalist, principal songwriter, and guitarist of the punk rock band Green Day, which he co-founded with Mike Dirnt. Armstrong is also a guitarist and vocalist for the punk rock band Pinhead Gunpowder and provides lead vocals for Green Day's side projects Foxboro Hot Tubs and The Network.

Raised in Rodeo, California, Armstrong developed an interest in music at a young age, and recorded his first song at the age of five. He met Mike Dirnt while attending elementary school, and the two instantly bonded over their mutual interest in music, forming the band Sweet Children when the two were 15 years old. The band changed its name to Green Day, and would later achieve massive commercial success. Armstrong has also pursued musical projects outside of Green Day's work, including numerous collaborations with other musicians.

In 1997, to coincide with the release of Nimrod, Armstrong founded Adeline Records in Oakland to help support other bands releasing music and signed bands such as The Frustrators, AFI and Dillinger Four. The record company has since come under the management of Pat Magnarella and is now based in San Diego.