The Ottoman Caliphate, under the Ottoman Dynasty of the Ottoman Empire inherited the responsibility of the Caliphate from the Mamluks of Egypt.
During the period of Ottoman growth, Ottoman rulers beginning with Mehmed II claimed the caliphal authority. His grandson Selim I, through conquering and unification of Muslim lands, became the defender of the holiest places in Islam. The demise of the Ottoman Caliphate took place in part because of a slow erosion of power in relation to Europe and end of the state in consequence of partitioning of the Ottoman Empire. Abdul Mejid II, who lost the Sultanate, kept the Caliph position for a couple of years, but with Atatürk's reforms, the caliph position was abolished.
Read more about Ottoman Caliphate: Insignia