I wish the answer to this were more existential, and thus more interesting. Alas, it’s as simple as this: a corporation becomes a corporation when you duly file Articles of Incorporation, also know as charter documents, with the state official authorized to recognize and process such filings. In California, that’s the Secretary of State. In Delaware, it’s the Division of Corporations. Same for LLCs, except that formation document tends to be called Articles of Organization.