Kjetil Tvedte Grutle, better known as Grutle Kjellson, is a Norwegian musician, best known as the bassist and vocalist of the Norwegian extreme metal band Enslaved. Kjellson and guitarist Ivar Bjørnson are the founding and only constant members of the band, as well as the main songwriters. He has released sixteen studio albums with Enslaved and won five Norwegian Spellemann Awards with the band.

RIITIIR, occasionally typeset as "RIITIIЯ," is the twelfth studio album by Norwegian extreme metal band Enslaved. It was released on September 28, 2012 in Europe and on October 9, 2012 in North America. The name RIITIIR is Ivar Bjørnson's "Norse-ified" take on the words "Rites/Rituals", or "The Rites of Man", and rituals form the central concept of the album. The album received positive reviews from music critics, and sold around 2,300 copies in its first week of release in the United States, which made it their highest debuting album to date in terms of sales.