Final answer:
Muhammad al-Mahdi was the last imam for the Shi'ites in 900 AD.
Step-by-step explanation:
The last imam for the Shi'ites in 900 AD was Muhammad al-Mahdi. The Twelvers, who make up about 95 percent of the Shia, believe that Muhammad al-Mahdi is the twelfth and final imam chosen by God. He went into 'mystical hiding' in the ninth century and is believed to return one day to defeat evil and herald the Day of Judgment.