Historically, Prophet Muhammad and the Caliphs were considered the leaders of Islam (particularly Sunni Islam when the Caliphs are considered). However, The Caliphate was abolished in the early 1900s and Islam remains leaderless on worldwide level.
The leader of Islam Is Muhammad.
Prophet Muhammad(peace be upon Him) is the leader of Islam.
Islam is not an organization. Thus we can't say who is the leader. Muslims believes in one god(Allah), and muhammed is the messenger of Allah and he is the one and only prophet Islam of this time.