Twelver Shi'a Islam, also known as Ithna Ashariyyah, is the largest branch of Shia Islam and believes in a succession of twelve imams, starting with Ali and ending with the hidden Imam Mahdi, who they believe will return as a messianic figure. This branch emphasizes the importance of the imamate and the leadership of these twelve divinely ordained leaders in guiding the Islamic community in spiritual and religious matters.