Who is a Custodian of the Two Holy Mosques?

It is a historical term which refers to King of Saudi Arabia. Custodian of the Two Holy Mosques is a pious title first adopted by the Ayyubids, Mamluk Sultans of Egypt, the Ottoman Sultans and which has been revived by modern Saudi kings. This means that King of Saudi Arabia in his role as protector of the two holiest cities of Islam, Mecca and Medina, which had traditionally been the role of the Caliph. First Saudi king to assume the title was Fahd bin Abdul Aziz in 1986. The reigning king, Abdullah bin Abdul Aziz, has taken the same title after the death of King Fahd, his half brother, in 2005.