A zoologist was a scientist that studied animals. Their branch of biology was called zoology.
The Doctor showed himself to be a zoologist in his first, (TV: The Ark) third, (TV: The Silurians) fourth, (TV: The Ark in Space) sixth, (AUDIO: Bloodtide) seventh, (TV: Blood Heat) eighth, (AUDIO: Wirrn Dawn) ninth, (TV: Only Human) tenth, (TV: Tooth and Claw) eleventh, (TV: Dinosaurs on a Spaceship) and twelfth incarnations. (TV: Listen)
Bracebridge Hunz was an entertainer and a celebrated zoologist in Victorian London. (PROSE: The Lampblack Wars)
Professor Vittorio Levi was a zoologist, botanist, astronomer, anthropologist and amateur space traveller, and also a colleague and friend of the Doctor. He, Sarah Jane Smith and the Fourth Doctor travelled to the planet Aquatica where they were taken hostage by Medusians. (PROSE: War on Aquatica)
Luis Vittorino was a zoologist who directed the removal of the Hammies skeletons. (PROSE: The Tree of Life)
Dr Smith was brought to Zamper to research why the productivity of the Zamps had been decreasing for the last couple of decades. (PROSE: Zamper)