John Lennon was an English singer-songwriter and peace activist who was the co-founder of the Beatles. He is best known for his song 'IMAGINE', which has become an anthem for peace and unity. Lennon wrote and performed the song in 1971, and it has since been covered by many other artists. Lennon's solo career was also successful, with several albums and singles reaching the top of the charts. He was tragically killed in 1980, but his legacy lives on through his music.