An influencer is an individual who has above-average impact on a specific niche process.
Influencers are normal people, who are often connected to key roles of media outlets, consumer groups, industry associations or community tribes. Influencers may or may not be aware of your company, but represent control of an audience segment that is important to your business.
Such individuals are not simply marketing tools, but social relationship assets. They may be the person responsible for affecting key contracts, supporting new product releases, or part of a resource pool that increases market awareness and industry shifts before they happen.
In the end, influencers are a key type of evangelist for your company.