One who conducts research. In the field of scientific research, also called an investigator or scientist.

is a Virginia Tech employee (i.e., anyone who receives compensation for their work) conducting research in a laboratory or group of laboratories under the direction of a Principal Investigator who is responsible for the daily operations of a laboratory or group of laboratories.

a scientist who devotes himself to doing research

a person who conducts research at the licentiate level or higher and whose work requires extensive use of the collections or archives material in the Library of Parliament

Another word that can be used for "investigator". An investigator may or may not be a doctor.

The individual who conducts and directs the study and carries the primary responsibility for the research. The Researcher is referred to as the Principal Investigator when acting as the leader of a research team.

See Principle Investigator (PI)