Imam Mahdi is a figure in Islamic eschatology who is believed to appear at the end of times to rid the world of evil and injustice. He is said to be a descendant of Prophet Muhammad and will appear shortly before the Day of Judgment. The concept of Imam Mahdi is universal and is accepted by Islamic scholars. The Mahdi features in both Shia and Sunni branches of Islam, though they differ extensively on his attributes and status. Among Twelver Shias, the Mahdi is believed to be Muhammad al-Mahdi, son of the eleventh Imam, Hasan al-Askari, who is said to be in occultation (ghayba) by divine will. The belief in Mahdi of the lineage of the prophet is central to Shia Islam, in general, and to Twelver Shia, in particular, where Mahdi is identified with the twelfth Imam. Sunni and Shia traditions have much in common about the career of Mahdi, and both believe in several signs before his advent.