MrGreyOwl's republican title generator!
I got Grand Protector. And you?
Grand Chairman. Mao would be proud.
everything's probably taken already, but I'll try.
As far as English-derived titles go, maybe Ealdorman/Alderman.
Reeve or High Reeve is a possibility. Reeves were usually peasants who were given administration tasks in a feudal manor. I could see it being a president's title in a republic formed by a peasant uprising at an early point in English history.
Advocate or Advocate General.
IDK if someone mentioned naming them after famous republican leaders.
Prelate.
Premier
Speaker
Vox Populi
Archon
Vozhd works for a Slavic republic, especially a more militaristic one. It's used for Communist leaders in Russian but it generally means leader or master. It's been compared to Fuhrer as they both generally mean leader and imply both political and military power. It was used in reference to Stalin and Lenin (Vozhd of the Proletariat or Vozhd of the peoples). It was also used by Karađorđe during the 1st Serbian uprising. He was a peasant, and was actually "president of the governing council of Serbia" for a while. He could have made a republic (since he wasn't a noble, it's quite surprising that his descendants would be kings) and made Vožd the title of the head of state of the Republic of Serbia. Also, Vozhd is kind of like Doge, since it derives from the Slavic equivalent to Duke, which is Voivode/Vojvoda/Wojewoda (literally meaning military leader/warlord but generally translated to duke through its relation to the title
bellidux and its later use as a regular noble title). So Vozhd could be translated as Doge if it came to be used in a republican context.