Ildulb mac Causantín, anglicised as Indulf or Indulph, nicknamed An Ionsaighthigh, "the Aggressor" (died 962) was king of Alba from 954 to 962. He was the son of Constantine II; his mother may have been a daughter of Earl Eadulf I of Bernicia, who was an exile in Scotland. John of Fordun and others supposed that Indulf had been king of Strathclyde in the reign of his predecessor, based on their understanding that the kingdom of Strathclyde had become a part of the kingdom of Alba in the 940s. This, however, is no longer accepted.