In Islamic eschatology, the Mahdi (Arabic: مهدي‎ / ISO 233: mahdī / English: Guided One) is the prophesied redeemer of Islam who will rule for seven, nine or nineteen years- (according to various interpretations) before the Day of Judgment (yawm al-qiyamah / literally, the Day of Resurrection) and will rid the world of wrongdoing, injustice and tyranny.

In Shia Islam, the belief in the Mahdi is a "central religious idea" and closely related as the Twelfth Imam, Muhammad al-Mahdi, whose return from occultation is deemed analogous with the coming of the Mahdi.

In Sunni traditions, there are several hadith referring to the Mahdi.

See Islamic eschatology.

The Sunnis view the Mahdi as the successor of Prophet Mohammad, the Mahdi is expected to arrive to rule the world and he is to reestablish uprightness, harmony, and correct religion.
The definite term mahdi, means “the rightly-guided one”. The Mahdi is not mentioned in the Qurʾān, but rather in the Sunnah. Some hypothesise he came about when the Arabian tribes were settling in Syria under Mo’awiya. “They anticipated ‘the Mahdi who will lead the rising people of the Yemen back to their country’ in order to restore the glory of their lost Himyarite kingdom. It was believed that he would eventually conquer Constantinople.”