Specialist

An individual who has built-up a deep knowledge and understanding of a particular subject or subject area.

You can be a specialist in any number of subject areas, you don’t have to work in the industry of the applied subject area to be a specialist.

Many amateurs have made valuable contributions to the knowledge base of scientific and other fields.

A specialist can be comparable with an expert, however, the latter has gained their proficiency and knowledge from working within a particular industry, subject area or field of knowledge.