Final answer:
The Shia Muslims believe that only the Imams, who are direct descendants of Muhammad, can interpret the Qur'an. The Twelvers, a majority within Shia Islam, regard Ali as the first of twelve infallible Imams dictate religious guidance.
Step-by-step explanation:
The Shia or Shi'ite Muslims believe that only the Imams, who are considered to be direct biological and spiritual descendants of Muhammad's family, can interpret the Qur'an. In particular, the majority of Shia Muslims, known as the Twelvers, hold that there have been twelve infallible Imams, starting with Ali, Muhammad's son-in-law and cousin, who have been chosen by God. Ali is seen as the first legitimate Imam in contrast to the title of 'caliph' and is believed to have been the succession's origin after the death of Muhammad.
The twelfth and final Imam, Muhammad al-Mahdi, is believed to have gone into 'mystical hiding' and will return to defeat evil and herald the Day of Judgment. This distinctive belief in the role of the Imam sets Shia Muslims apart from Sunnis, who constitute the majority of Muslims and do not attribute divine appointment to the line of Twelve Imams, believing instead that any pious man following Muhammad's example could lead.