What the office is built out of. Each state's insurance code creates the office and sets its powers, and the details are genuinely local. Oklahoma's statute requires that the Insurance Commissioner "shall be at least twenty-five (25) years of age and a resident of the State of Oklahoma for at least five (5) years, and have had at least five (5) years' experience in the insurance industry in administration, sales, servicing or regulation," and adds a conflict rule: the Commissioner "shall not be financially interested, directly or indirectly, in any insurer, agency or insurance transaction except as a policyholder or claimant under a policy." How the office is filled varies too, and the statutes say so directly. Section 12900 of California's Insurance Code provides that "the commissioner shall be elected by the people in the same time, place, and manner as the Governor not to exceed two four-year terms." New York's Financial Services Law provides instead that the superintendent "shall be appointed by the governor, by and with the advice and consent of the senate, and who shall hold office at the pleasure of the governor." So the office is elective in some states and an appointment in others, and the statutory qualifications, where any exist, are the state's own.
The NAIC is the coordinating body, not the regulator. The National Association of Insurance Commissioners is the association of these state officials. It writes model acts and model regulations, runs accreditation programs and maintains shared systems, and none of that binds anyone until a state legislature enacts it. This matters for reading anything about insurance law, including the material on this site: a rule quoted from an NAIC model act describes what the association recommends, and the version in force where you live may differ or may not exist. It also explains a common confusion in search results, where "insurance commissioners" almost always refers to the association's name rather than to any individual regulator.
What the office does that a consumer can use. Four functions matter most in practice. It licenses: an insurer must be admitted to do business in the state, and a producer must hold a license with the right lines of authority, both of which are verifiable through the department. It supervises solvency, and it is the commissioner who petitions a court to place a failing insurer in rehabilitation or liquidation, which is also the event that activates the state guaranty system. It regulates market conduct, including how policies are sold and how claims are handled, and can fine, suspend or revoke a license. And it takes complaints, which is the practical point: a policyholder who believes a claim was wrongly denied, or that a policy was misrepresented at sale, has a free administrative route that does not require a lawyer.
What it does not do. The office is not a court and does not award damages. A complaint typically results in the department requiring the insurer to explain its position in writing against the policy language and the state's claims-handling rules, which is frequently enough to resolve a dispute and is never a substitute for a contract claim. Nor does the office set prices in most lines: rate regulation ranges from prior approval to file-and-use to no rate filing at all depending on the state and the line of business.
Where compensation fits. The commissioner is the official who licenses the people who sell insurance, and state law is where the rules on how those people may be paid live. NAIC's producer licensing model act bars an insurer or producer from paying "a commission, service fee, brokerage or other valuable consideration" to an unlicensed person who was required to be licensed, and bars an unlicensed person from accepting one. Some states go further, with disclosure requirements where a producer takes compensation from both the customer and the insurer. A buyer who wants to know how the person selling them a policy is paid is asking a question the state has already legislated about, and the department is where the answer and the enforcement live.