Ambassador
Also known as: brand advocate
A brand ambassador, also known as a brand advocate, is someone who acts as an advocate for a product, brand or company. The ambassador can be either a paid employee of the company itself or an enthusiastic loyal customer. Usually the latter category is meant. An ambassador who is employed by the company is often called a brand evangalist.
A brand's fans are an important asset for brand awareness and acquisition, such as through word of mouth. Ambassadors are not only a satisfied and loyal users of a product. They will also point out to others the benefits of the product and the values of a brand. When criticized, they will defend the brand.
The most important way to build a group of ambassadors around your brand is to develop products and services that people will love and optimize the customer journey. Some companies encourage satisfied customers to act as ambassadors by offering perks, such as loyalty programs, fan clubs and perks for bringing in new customers, and using communication to encourage them to share certain information with their friends, such as through social media.
An example of a brand that benefits greatly from its loyal fan base of ambassadors is Apple.