Early legal references to corporate-like bodies appear in ancient codes (including traditions traced to Mesopotamian law). Roman civil law developed religious, governmental, and society forms. Under the Roman Empire the idea grew that a corporation exists only by the sovereign’s creative act—and with approval comes control. Offshoots include canon law and modern civil law.
Canon law, dealing with church property, produced the corporation sole (one person, e.g. a bishop) and the corporation aggregate (many persons).
In the early thirteenth century, Pope Innocent IV developed the corporation as a persona ficta—a fictitious or artificial person created and controlled by papal authority. That separated the corporation (artificial person) from a man. “Corp” means body. Everyday English and legal language diverge: the same word can mean different things. “Legal” itself points to fiction. Murder is unlawful; a state may still issue a legal licence to kill. In ordinary speech you and I are persons; in law a “person” may mean a corporation or partnership—an artificial public entity.
“A corporation derives its existence and all of its powers from the State and, therefore, has only such powers as the State has conferred upon it.” Power here means legal capacity to fulfil the objects for which it was created, sourced in charter and statute.
When governments themselves incorporate, they step into the same category of creatures they create—subject to commercial rules foreign to living sovereignty. See What Is a “Person”? and Your Sovereignty.