haha really? ok give me a few minutes i will give you a non-exhaustive list:
mubarak
mugabe
qaddafi
mao
stalin
george iii
antonio lopez de santa anna
napoleon
edward I
good ole ghenghis
leopold of belgium (fucking hate this guy)
ivan the terrible
henry viii
and these dudes, who served less time, but really fucked the place up in their tenure:
hitler
nero... in fact all those shitty roman emperors (see comments regarding succession problems)
emperor qin
vlad the impaler
keep in mind, these are just the really really awful ones.
there are countless others who really weren't good people at all, they just didn't stand out.
compare fucking calvin coolidge or james madison to mussolini or emperor qin: there is no comparison at all. none.
you can name elected leaders who were shitty, yes, anyone can. people are generally shitty. but the thing is, as people have said, these people leave. if they stay on past their term, they are now a dictator. in a "dictatorship" society, this is acceptable. in a democratic society it is not and you will see military intervention/international intervention hopefully.
name some good dictators. and i mean actually good. not like "oh he massively expanded country X's borders" no. i dont give a shit about that. you're talking about a murderer.
a genuinely benevolent dictator who improved the world. improved it on purpose not improved in the sense that, say, ghenghis facilitated the silk road. not talking about that. talking about, one day, they say "you know for the good of mankind i think we should probably cut the size of our army, or send our doctors to help cure that disease over there."
go. i bet you all my diplopoints that i can match anyone you bring up with a president/pm who was better.
and keep in mind, democracy hasn't been around that long. you have all of history to choose from, i only have a few hundred at most, you have thousands and thousands.