"Dies irae" is a Latin sequence attributed to either Thomas of Celano of the Franciscans (1200–1265) or to Latino Malabranca Orsini, lector at the Dominican studium at Santa Sabina, the forerunner of the Pontifical University of Saint Thomas Aquinas in Rome. The sequence dates from the 13th century at the latest, though it is possible that it is much older, with some sources ascribing its origin to St. Gregory the Great, Bernard of Clairvaux (1090–1153), or Bonaventure (1221–1274).

Thomas of Celano was an Italian friar of the Franciscans as well as a poet and the author of three hagiographies about Francis of Assisi.