Which of the following is required for an insurer to operate legally in Colorado?

For an insurer to operate legally in Colorado, obtaining a certificate of authority from the Commissioner is essential. This certificate acts as a license issued by the state that grants the insurer the permission to conduct insurance business within Colorado. It ensures that the insurer has met all regulatory requirements, demonstrating that they are financially stable and compliant with state laws, thus protecting policyholders.

The other options do not represent legal requirements for an insurer's operation. An advertising permit is not a requisite for engaging in insurance business, as advertising regulations differ from operational licensing. Similarly, there is no mandated minimum number of agents that an insurer must have to be legally licensed in the state. Lastly, while third-party compliance reviews may be beneficial for an insurer's internal processes, they are not a requirement for obtaining the necessary legal authority to operate in Colorado.