A generalissimo is a commissioned officer of the highest rank; the word is often translated as "Supreme Commander" or "Commander in Chief". It is a Spanish superlative substansive (generalísimo), meaning that it can function either as a noun or as an adjective. When used as a noun, the correct sense is "General to the Nth degree" (or commander in chief of the entire armed forces of a specific country); as an adjective, the closest English form is "most general", but the concept is best expressed by the grammatically incorrect expression "most generalest".

The D Francisco Franco, Chief of State of the Spanish State, also held the title Generalísimo de los Ejércitos Españoles, or "Generalissimo of the Spanish Armies", a title which expressed his supreme command of the Army, Navy, and Air Force of the Spanish State.

The Japanese equivalent to this was a Shogun.