Nachtmystium was an American black metal band formed by Blake Judd, formerly known as Azentrius, and Pat McCormick. The band's name is derived from the German word Nacht meaning "night", and the made-up term mystium which resembles the Latin adjective mysticum. Judd and McCormick combined the words to create the band's name, which they state means "Encompassing Darkness". Nachtmystium released multiple critically praised albums between 2005 and 2012, including Instinct: Decay (2005), Assassins: Black Meddle, Part I (2008), and Silencing Machine (2012). Controversy marred the band's success in 2013 when Judd was arrested for theft charges and publicly admitted he had a severe drug problem. After nearly four years of inactivity, Nachtmystium returned in 2017 and released a new EP, Resilient, in 2018. However the band would be disbanded in June 2020 by Blake after a lengthy final post on the official Facebook page.

Nachtmystium's line-up has frequently changed since its formation. Furthermore, while the band originally started as a black metal band, and even toured with black metal acts such as Angelcorpse, Goatwhore and Watain, Judd has frequently stated that the band should not be considered black metal per se. In an interview with DEAF SPARROW Zine, Judd stated, "What separates us from your average black metal band is that we're NOT a black metal band, we're a 'do-whatever-the-fuck-we-want' metal band and black metal happens to be what we build our foundation off of (in the case of Instinct: Decay and its predecessors), if you must categorize the rhythm sections of our music (rhythm guitars, bass and drums — the core of any album)." J. Bennet of Decibel Magazine described the band's sound as "Blackadelia". Jason Bracelin, of the Las Vegas Review-Journal, compared the band's latter work to Pink Floyd, claiming, "[Assassins] is what happens when Pink goes black." Since the release of Assassins, the band has received additional press-coverage and attention from media outlets, including Metal Maniacs, Terrorizer, CMJ New Music Monthly, and Metalkult.com. Despite their departure from the black metal genre, Carlos Ramirez of IGN.com listed Assassins as one of the ten greatest black metal albums.

Judd recruited Chris Black to produce Nachtmystium's later albums and compose lyrics. Black's themes and lyrics from Addicts: Black Meddle, Part II were inspired by Judd's heroin addiction. Judd assumed songwriting duties for Nachtmystium's final studio album, The World We Left Behind, and included many lyrics about his personal struggles with addiction. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.