Mehmed V Reshad (1844–1918) was the 35th Ottoman Sultan, reigning from 1909-1918. He also served as the Caliph of Empire. Mehmed personally wielded very little actual authority in his country. His reign coincided with World War I, which his country entered on the side of the Central Powers. It is also during his reign that the Armenian genocide began.
Mehmed died months before the war ended, and he did not live to see his empire's collapse.
Mehmed V is not specifically referenced in text, but simply referred to as "the Sultan". The fact that Abdul Majid II is confirmed to be Sultan in The Center Cannot Hold suggests that his historical predecessor, Mehmed, held the throne.