The events following the death of the Prophet Muhammad demonstrate that there is no singular leadership in the Islamic tradition, except within the Shia branch of Islam. Only Shia Islam has adopted the concept of imamate, which elevates its leader to the position of a grand imam, believed to be the rightful leader of the entire Muslim community.
In its most extreme form, Shia doctrine even questions the prophethood of Muhammad, suggesting that Ali bin Abi Talib—later referred to as Imam Ali—was the rightful prophet. Shia Islam traces its leadership through 12 imams, all descendants of Imam Ali and the Prophet’s family. To this day, Shia Muslims await the return of their hidden imam, Imam Mahdi, who is believed to be the true leader of the global Muslim community.
Therefore, outside of Shia tradition, there is no concept of a grand or supreme leader in Islam. Anyone claiming such a title outside the Shia context is merely a self-declared figurehead.
Translated from here.