Issuer is a special term for companies to issue bills such as stocks, bonds and convertible bonds, and it is generally the subject of issuing these bills. Generally speaking, the controlling shareholder and the actual controller are the same thing, but the legal subject is different. The controlling shareholder generally refers to a company or an enterprise, while the actual controller generally refers to a natural person. If you want to know more about the meaning of the three, I suggest you read the accounting book or the company law.