A middleman is someone who acts as a mediator between two parties in a transaction. Out of the options provided, the one who acts as a middleman is the "Agent." An agent is a person who is appointed to act on behalf of someone else, such as a manufacturer or a consumer. They usually facilitate the sale of goods or services between the manufacturer and the consumer by helping to negotiate the terms of the sale and ensuring that both parties are satisfied with the outcome. Therefore, an agent is a middleman in this scenario.