My recent entry on the Ruler of Egypt, Hakim the Mad, has led to a debate amongst the historians here in the society about the unkind sobriquets that attach to rulers. The obvious one that comes to mind is Ethelred the Unready, or perhaps Ivan the Terrible. I remember having an argument in a train with a History teacher about this. I suspect that I was arguing that History was a wonderfully entertaining diversion just as long as one looked at the unusual, grotesque, odd and amusing in the historical record. I ended up challenging him to produce a list of silly names for Kings and rulers, such as Vlad the Impaler. He was nonplussed. Sound on the repeal of the Corn Laws no doubt, but quite at sea with the broad sweep of silliness in history
My reply was as follows: Pepin the Hunchback (Frankish Price), Otto the Idle (King of Prussia), Stephen the Fop (Bavarian Duke), Charles the Simple, Charles the Bad, Charles the Bald and Charles the Mad, Louis the Stammerer, Louis the Sluggard, Louis the Fat (son of Louis X1V) and Louis the Quarreler, Ferdinand the Inconstant, Henry the Impotent (prince of Castile), Ivan the Terrible, Pedro the Cruel (King of Castile),Gorm the old (Denmark, d940) and Harald Bluetooth.(Denmark 935-985), Selim the Grim (sultan of Turkey)
On the subject of the reason for poor Ethelred the Unready receiving his unfortunate sobriquet, history comes up with three choices. The first is that he was badly advised (Unready having an archaic meaning to this effect), the second that he was ill-prepared, and the third that he inadvertently urinated into the christening font (as many babies have done before and since), thereby defiling the holy water and showing himself 'unready' (meaning unfit) to rule.
I feel sure there are more out there but books which merely list the kings of various countries are rather unfashionable these days.