Sultan vs. King: What's the ?

sultan kingSultan Ibrahim Ismail ibni al-Marhum Sultan Mahmud Iskandar al-Haj (Born 22 November 1958 – enthroned 23 January 2010 – ) Raja Zarith Sofia binti al-Marhum Sultan Idris al-MutawakilMaḥmūd of Ghazna (rened ad 998–1030) was the first Muslim ruler to be called sultan by his contemporaries, and under the Seljuqs of Anatolia and Iran it became a regular title.