A commander-in-chief, also sometimes called supreme commander, or chief commander, is the person or body that exercises supreme operational command and control over a nation's military forces. As a technical term, it refers to military competencies that reside in a nation-state's executive leadership—a head of state, a head of government.
Often, a given country's commander-in-chief (if held by an official) need not be or have been a commissioned officer or even a veteran. In these countries this follows the principle of civilian control of the military.
The formal role and title of a ruler commanding the armed forces derives from Imperator of the Roman Kingdom, Roman Republic and Roman Empire, who possessed imperium (command and other regal) powers.
In English use, the term first applied to King Charles I of England in 1639. It continued to be used during the English Civil War. A nation's head of state (monarchical or republican) usually holds the nominal position of commander-in-chief, even if effective executive power is held by a separate head of government. In a parliamentary system, the executive branch is ultimately dependent upon the will of the legislature; although the legislature does not issue orders directly to the armed forces and therefore does not control the military in any operational sense. Governors-general and colonial governors are also often appointed commander-in-chief of the military forces within their territory.
A commander-in-chief is sometimes referred to as supreme commander, which is sometimes used as a specific term. The term is also used for military officers who hold such power and authority, not always through dictatorship, and as a subordinate (usually) to a head of state (see Generalissimo). The term is also used for officers who hold authority over an individual military branch, special branch or within a theatre of operations.
This includes heads of states who: