Twelver Shia Islam, also known as Ithna Ashariyya, is the largest branch of Shia Islam. It is characterized by the belief in a line of twelve Imams, who are considered the spiritual and political successors to the Prophet Muhammad. The first Imam is Ali ibn Abi Talib, the Prophet's cousin and son-in-law, and the twelfth Imam, Muhammad al-Mahdi, is believed to be in occultation and will return as a messianic figure. Twelver Shia Muslims follow the teachings of the Qur'an and the traditions of the Imams, emphasizing the importance of their guidance in understanding faith and law. They celebrate significant events such as Ashura, which commemorates the martyrdom of Imam Hussein, the grandson of the Prophet Muhammad, at the Battle of Karbala.