Mehmed the Conqueror
In the Ottoman history Mehmed, who seized Constantinople, is described as a brave, noble and resolute soldier, and it is true. However, chroniclers of Mehmed did not add, that the sultan was pathologically ruthless (they would be executed, if they did it). Mehmed was extremely ruthless. When his father, previous sultan, died, Mehmed invited his wife, and while he was civilly talking to her for several hours, the servants, sent by him, drowned the little son of the sultana... As his contemporaries say, Mehmed Fatih showed his cruelty in the seized Constantinople as well. When one of the conquered grandees refused to give his son to the harem, Mehmed ordered to kill the boy in front of the father, and then executed the father as well.
Suleiman the Magnificent
He was one of the most just, wise, and sober-minded sultans, and, in general, it was a rare characteristics of the Ottoman rulers. He is famous for his territorial expansions: his army beleaguered Vienna, he conquered Persia and Egypt. Sultana Roxelana from Ruthenia was one of his wives. To please her, Suleiman ordered to strangle his elder son from another wife: Mustafa was killed in front of him. After it, he ordered to kill the children of his son, including a 5 years old boy.
Abdul Hamid II
This sultan ruled the empire during the decline of its might. Trying to prevent the inevitable collapse of the empire, Abdul Hamid committed terrible crimes. During his rule, the first mass massacre of the Armenian (300,000 people died in several days in Anatolia in the end of the 19th century) occurred: it was done to draw away the attention of the population from the internal problems. The sultan was not more kind to his subjects-Turks. His contemporaries say, that in the beginning of the 20th century Istanbul was full of spies and killers, who murdered those, who hindered the sultan. Then, following the direct order of Abdul-Hamid II, the residents of Istanbul, who organized a demonstration, demanding some liberties, were shot. As a result, the empire decayed. The defeat during the World War I was necessary for Turkey to fall and rise again.