Although he was not the founder of the band, Mikael Åkerfeldt is the only member to appear on every release. He is Opeth's main songwriter and lyricist and has defined much of the band's sound. Åkerfeldt was influenced at a young age by heavy metal bands such as Slayer, Death, Black Sabbath, Celtic Frost, King Diamond and Morbid Angel. Åkerfeldt was later influenced by progressive rock and folk music, both of which had a strong impact on the sound of the band. Opeth's distinct sound combines elements of heavy metal with acoustic passages and elements of progressive metal and progressive rock. Åkerfeldt commented on the diversity of Opeth's music: