Imam Mehdi will appear at the end of times to rid the world of evil and injustice. In Islam, it is believed that he will appear alongside the prophet ʿĪsā and establish the divine kingdom of Allah on Earth. He (Mehdi) will be from the family of Prophet Muhammad (ﷺ),
"The Mahdi is one of us' Ahl al-Bait (the prophet's family) and Allah will prepare him in one night." (Musnad Ahmad: 645)
The Prophet said: "The Mahdi will be of my stock, and will have a broad forehead [and] a prominent nose. He will fill the earth with equity and justice as it was filled with oppression and tyranny, and he will rule for seven years." (Sunan Abu Dawud)