Final answer:
In Shi'ism, the Imam is a spiritual and religious leader who holds great authority. They are believed to be the source of definitive religious guidance and have the final word on religious doctrine. The Shia believe in twelve infallible Imams, the last of whom is expected to return with Jesus.
Step-by-step explanation:
In Shi'ism, the figure of the Imam holds great spiritual and religious authority. The Shia believe that Ali, the son-in-law of Muhammad, was the first legitimate Imam and that the line of Imamate continued through twelve infallible leaders. They believe that the twelfth Imam, Muhammad al-Mahdi, went into hiding and will return with Jesus to establish justice on earth. The Imams are seen as the source of definitive religious guidance and have the final authority on religious doctrine.