Final answer:
In Shia Islam, Ali is considered the first legitimate Imam, a divinely guided protector who can introduce new laws and is part of a line of twelve infallible Imams.
Step-by-step explanation:
After the death of the Prophet Muhammad, the question of succession led to differing opinions and practices among Muslims. Ali, Muhammad's cousin and son-in-law, is regarded by Shia Muslims as the first legitimate Imam. The Imam is seen much more than a political leader; he is considered a divinely guided protector, capable of introducing new laws and able to receive guidance, though not in a prophetic manner like Muhammad. According to Shia beliefs, Ali passed on this spiritual leadership to a line of twelve infallible Imams, with the belief that the final Imam will return to defeat evil.