George Henry Crumb Jr. was an American composer of avant-garde contemporary classical music. Early in his life he rejected the widespread modernist usage of serialism, developing a highly personal musical language which "range[s] in mood from peaceful to nightmarish". Crumb's compositions are known for pushing the limits of technical prowess by way of frequent use of extended techniques. The unusual timbres he employs evoke a surrealist atmosphere which portray emotions of considerable intensity with vast and sometimes haunting soundscapes. His few large-scale works include Echoes of Time and the River (1967), which won the 1968 Pulitzer Prize for Music, and Star-Child (1977), which won the 2001 Grammy Award for Best Contemporary Classical Composition; however, his output consists of mostly music for chamber ensembles or solo instrumentalists. Among his best known compositions are Black Angels (1970), a striking commentary on the Vietnam War for electric string quartet; Ancient Voices of Children (1970) for a mixed chamber ensemble; and Vox Balaenae (1971), a musical evocation of the humpback whale, for electric flute, electric cello, and amplified piano.

Black Angels, subtitled "Thirteen Images from the Dark Land", is a work for "electric string quartet" by the American avant-garde composer George Crumb. It was composed over the course of a year and is dated "Friday the Thirteenth, March 1970 " as written on the score. The Latin phrase in tempore belli, in time of war, written into the score by Crumb is a reference to the Vietnam War taking place at the time when Black Angels was composed.