A biologist was a type of scientist who specialized in the field of biology.
Klingon advocate Kolos was encouraged by his parents to take up the law, rather than to become a soldier. His parents, too, took up a professional role in Klingon society, as his father was a teacher and his mother was a biologist at the university. (ENT: "Judgment")
Captain James T. Kirk requested a biologist to be assigned to the landing party that transported down to the planet Omicron Ceti III in 2267. (TOS: "This Side of Paradise")
During the mid-2260s, James T. Kirk's brother, Sam, worked as a research biologist on Deneva, where he maintained his own laboratory. (TOS: "Operation -- Annihilate!")
Randi Bryce served as the ship's biologist aboard the USS Ariel in 2269. (TAS: "The Eye of the Beholder")
Types of biologists