Throughout history, the executive authority of a republic or commonwealth has adopted many names. Here is a brief sampling, in chronological order. Note that not all of these examples of republics are democratic republics.

• Consul ("Councillor," ancient Rome; two consules ruled jointly.)
• Pope ("Father," Catholic Church and Vatican. Yes, it's a republic. Think about it.)
• King ("Kinsman," early Teutonic feudal nations; these nations originally elected their leaders.)
• Duke ("Leader," Renaissance Venice et alia.)
• Lord Protector (English Interregnum; first modern democratic republic executive.)
• Governor (Each of the United States, which are republics or commonwealths in their own right.)
• President ("One who presides;" Federation of the United States, Republic of France, and almost every democratic republic which has since been organised.)
• Chancellor or Kanzler (literally, "officer of the Chancery" or department of equity; Germany and Austria, and the Klingon Empire in Star Trek. Although everyone referred to Hitler as Führer, his official title was Bundeskanzler.)
• Ayatollah ("Sign of God;" Iran. Iran also has a President, who functions as head of government while the Ayatollah acts as head of state.)

If you can think of any more, or if I'm wrong about something, please feel free to /msg me.