Hannson & Karlsson were signed by Polydor, playing progressive Hammond organ based music and releasing three albums between 1967 and 1969. They became immensely popular in their home country and Europe, and even reached the ear of Jimi Hendrix, who took time out from his tour to jam with the duo, along with George Clemons on drums and Georg Wadenius on guitar, at the Klub Filips in Stockholm in late 1967. Hendrix went on to record a Hansson song, "Tax Free". The music can be defined as instrumental jazz-rock and psychedelia and the band setting was limited to the drums and organ, without vocals.
Hansson is probably best known for his musical interpretation of Tolkien's "Lord of the Rings", entitled 'Music Inspired by Lord Of The Rings. Released on Charisma Records after gaining a cult following in Britain due to import copies filtering over from Sweden, the album was his biggest success, reaching the Top 20 on the UK Album Charts in 1972.
Due to his pioneering work with both Hansson & Karlsson and his solo excursions into space rock, in recent years Hannson received the status of a living legend in his native Sweden.