From Destinypedia, the Destiny wiki
The Deathsong was a creation of Hive Wizards to corrupt, kill, and utterly destroy those who listened to it. The song was originally known as the Song of Life and was sung by the Ammonites, who had been gifted its notes by the Traveler. During the Hive-Ammonite War a choir of Wizards stole the song and began to sing it in order to unravel its secrets, although the origins of the Song of Life from the Light caused the Song to hurt and corrupt the Darkness infused Hive. After centuries, The Stricken finally found a way to corrupt the song using hidden notes within it and created the Deathsong, establishing a new class of Wizards known as Deathsingers.
Later, after the events of Shadowkeep, The Guardian, with the assistance of Eris Morn and guidance of Toland, the Shattered, would go to search and weaponize a Deathsong from Ir Airâm, Deathsinger and her choir to form a rocket launcher known as Deathbringer.
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