Ṣaʿb Dhu Marāthid (also al-Ṣaʿb b. Dhī Marāthid) was a mythical figure described in the medieval Islamic tradition as the tenth South Arabian king of the Himyarite Kingdom.
Traditions of Sa'b are largely derivative from those about Alexander the Great in the tradition of the Alexander Romance. As such, he followed Alexander in being identified with the Quranic figure of Dhu al-Qarnayn by some writers, notably Ibn Hisham.