Nothing in particular, but if it is a prophet, it is "alaihiisalam (as), and specially for the Prophet Muhammad (saw) it is "sallalahu-allaihwassalum (saw)." Missionaries are called Imams.
The leader of the Nation of Islam (NOI) is a man named Louis Eugene Wolcott who is better known as Louis Farrakhan Muhammad Sr.
Muhammad is said to be the founding leader and prophet of Islam
Allah is considered as the creator of all things, also known as God.
Prophet Muhammad (peace be upon him) is the original leader of Islam.
Islam is a religion not a spiritual leader. Islam is not dead.
Islam daily leader is called Imam who leads Muslims on praying for God.
The leader of Islam is prophet Muhammad (peace be upon him) and started in Mecca (or Makkah) in Saudi Arabia.
The original leader of Islam religion per Quran revelation by God is prophet Muhammad (peace be upon him)
King Solomon was not a follower of Islam. The king known for his wisdom was the son of King David, and leader of Israel. Despite not being a Muslim, King Solomon is regarded by Islam as an elect by God and a wise king.
Islam
The leader of Islam after prophet Muhammad (peace be upon him) is Abou Bakr Assedique (may God be pleased with him).
As far as I am aware Islam does not have a single spiritual leader, in the same way that Christianity has the Pope. Until the end of the Ottoman Empire (1918) the sultan of the Ottoman Empire was the de facto spiritual leader of Islam.