O

O (often stylized as ◯) is an Italian post-black metal and sludge project formed in Biella in 2010. They represent a specific intersection of the European extreme metal scene where the raw, misanthropic spirit of black metal meets the crushing weight of sludge and the atmospheric breadth of post-rock.

Their early work, exemplified by 'Il vuoto perfetto', established a foundation of dissonant, mid-tempo black metal, but it was their later output, particularly 'Antropocene', that solidified their reputation for exploring environmental and existential collapse. Musically, they are characterized by dense guitar layering, a preference for cavernous reverb, and a rhythmic approach that favors power over speed. They are frequently associated with the broader 'post-black' movement but maintain a grittier, more industrial edge than their more melodic contemporaries. Critical consensus highlights their ability to maintain a sense of genuine danger and discomfort even within complex, multi-part song structures. They occupy a niche space popular with fans of the 'Orthodox' black metal sound who also follow labels like Neurot or Consouling Sounds.