I Must Be the Devil is the album of songs that Kristín Anna Valtýsdóttir carried with her for more than a decade. A founding member of múm, she began performing her piano songs in 2006, alongside more experimental electronic work under the name Kría Brekkan. The nine pieces here were written for piano and voice between 2005 and 2017, and she has called them a private affair, made for emotional and spiritual survival. The record came out in April 2019 on Bel-Air Glamour Records, the label of Ragnar Kjartansson, together with The Vinyl Factory.

The album was recorded over four years with Kjartan Sveinsson, formerly of Sigur Rós, who produced it and plays electric piano, organ, bass and vibraphone on several tracks. Birgir Jón Birgisson shared the recording and did the mix. Cellist Gyða Valtýsdóttir appears on most of the songs, joined by a small string group of violins and viola. Kjartansson, in whose video installation The Visitors she had performed in 2012, sings backing vocals and co-directed the video for Forever Love. According to Kjartansson, the album was produced and financed by her friends in the music and visual art scene.

Kristín Anna plays piano throughout and adds vibraphone, celesta, organ and harpsichord. The Oceanwave Rocks My Kneeshells opens with cello and electric piano under her voice, and Forever Love is a plain piano ballad lifted by strings. Star, Child, almost seven minutes long, builds a soft chorus of backing voices over violins, viola and cello. The second side turns darker in colour: double bass, glockenspiel and vibraphone on Clay and Vapour, organ, harpsichord and guitar on In the Air. The closing Girl runs past eight minutes, the most open structure on the record.

Kjartansson presented it as "a big record full of deep truths, suffering, irony and beauty." Reviewing it for Pitchfork, Sophie Kemp compared her voice to Joanna Newsom and early Kate Bush and found the album gentle to a fault. She singled out Girl as its strongest moment, "a vast expanse dotted with strange futuristic sounds." The gatefold artwork plays on the censored original cover of Jimi Hendrix's Electric Ladyland, with a hidden Kjartansson to find among the figures.

Single LP on black vinyl in a gatefold sleeve with CMYK printed inner panels, issued in an edition of 500 copies (Bel-Air Glamour BA04 / VF230).