Which insurer must have at least $10,000,000 in capital and surplus and be established for at least 10 years?

The requirement that an insurer must have at least $10,000,000 in capital and surplus and be established for at least 10 years specifically pertains to an alien insurer. In the context of insurance, an alien insurer is one that is incorporated or formed under the laws of a foreign country and does business in the United States.

The reason for these stringent requirements is to ensure that the insurer is financially stable and has a proven track record before they can operate in the surplus lines market, which often deals with risks that standard insurers may not cover. This financial threshold and operational history are crucial in maintaining confidence in the insurer's ability to handle claims, particularly in a market where the risks are higher and less predictable.

Domestic insurers, which are based within the same state where they operate, and foreign insurers, which are from other states within the U.S., will have different regulatory and financial requirements specific to their jurisdictions. Mutual insurers, owned by policyholders rather than shareholders, also have their own unique criteria and do not inherently require the same capital and surplus levels as alien insurers. Thus, the specifications given in the question directly align with the definition and operational standards of an alien insurer.