Custodian of the Two Holy Mosques, or Protector of the Two Holy Cities, is a royal style that has been used officially by the monarchs of Saudi Arabia since 1986. The title has historically been used by many Muslim rulers in the past, including the Ayyubids, the Mamluks, the Ottomans and the Sharifain rulers of Hejaz. The title was sometimes regarded to denote the de facto Caliph of Islam, but it mainly refers to the ruler taking the responsibility of guarding and maintaining the two holiest mosques in Islam: Al-Haram Mosque in Mecca and the Prophet's Mosque in Medina, both of which are in the Hejazi region of Saudi Arabia. The Custodian has been named the most powerful and influential person in Islam and the Sunni branch of Islam by The Muslim 500, as well as the most powerful Muslim and Arab ruler in the world.

The King of Saudi Arabia, officially the King of the Kingdom of Saudi Arabia, is the monarch and head of state/government of the Kingdom of Saudi Arabia who holds absolute power. He is the head of the Saudi Arabian royal family, the House of Saud. The king is the supreme commander-in-chief of the Royal Saudi Armed Forces and the head of the Saudi national honors system. The king is called the "Custodian of the Two Holy Mosques", a title that signifies Saudi Arabia's jurisdiction over the mosques of Masjid al-Haram in Mecca and Al-Masjid an-Nabawi in Medina. The title has been used many times through the history of Islam. The first Saudi king to use the title was Faisal; however, King Khalid did not use the title after him. In 1986, King Fahd replaced "His Majesty" with the title of Custodian of the Two Holy Mosques, and it has been since used by both King Abdullah and King Salman. The king has been named the most powerful and influential Muslim and Arab leader in the world according to the Muslim 500.