St-Calais was a Norman, and a native of Bayeux; he may have been a member of one of its clerical dynasties. His mother's name, Ascelina or Anselma, is given in Durham's records; his father, whose name is unknown, became a monk at the monastery of Saint-Calais in Maine, and may previously have been a knight. Although St-Calais is generally referred to as Saint Calais or St-Calais, the main source of information about his life, the monastic chronicle of Symeon of Durham, does not call him such.