Final answer:
The person with direct responsibility for all aspects of a product line or brand is the product manager.
Step-by-step explanation:
The person who has direct responsibility for all aspects of a product line or a brand including the marketing mix is the product manager. The product manager is responsible for developing, implementing, and managing the marketing strategies and plans for the product or brand. They analyze market trends, conduct market research, set pricing, develop promotional campaigns, and coordinate with other departments such as sales and finance.