I like a good nickname. Today the best ones seem to belong to athletes, but royalty used to have some pretty sweet ones too. I don’t know much about the Byzantine emperors, but in my Western Civ textbook I’ve found two emperors with good nicknames: Constantine VII Porphyrogenitos (Wikipedia translates this “purple-born,” which is OK, but I like the way that the Greek sounds) and Basil II the Bulgar-Slayer (disclaimer: I have nothing against Bulgars). Basil’s nickname is a reminder that we are much more cautious about glorifying the killing of our enemies than people were centuries ago. It’s hard to see an American president wanting to be known for his animosity toward an entire people.
With the Ottoman Empire, lots of people now note that there’s a trope of “decline” after Suleiman’s death in 1566 that’s probably overstated. After all, the Ottomans nearly took Vienna in 1683 before the Poles came to the aid of the Habsburgs (Poland was repaid by Austria, Prussia, and Russia
partionining partitioning Poland out of existence in the 1700s). But there seems to have been a decline in leadership after Suleiman. Some of the nicknames of the great sultans: Mehmet the Conqueror, Selim the Inexorable (or the Grim), and Suleiman the Magnificent. Then, you’ve got Selim II the Sot. So when you go from the Magnificent to the Sot, that seems like a big part of the problem.