Dear friend, many thanks for your question, and I am happy to answer it through Meracareerguide. As you have asked the famous zoologist in the world, the list of few well known is as follows;
1. Aristotle: He was born in 384 BC and died in 322 BC. He was gifted, multidimensional scholar best known as one of the few most influential philosophers of the time. he was a renowned student of Plato and a famous teacher of Alexander The Great. He is considered the first zoologist to to classify the animal kingdom into two major groups of blooded and non blooded animals into young bearing, four footed animals, egg laying, birds and fish. He subdivided the non blooded animals into mollusks, crabs and insects. He wrote Histora Animalium, De Partbus Animalium and De Generatione Animalium. These works laid a solid foundation for the systematic study of animals or zoology for centuries to come.

2. Carl Linnaeus: He was born in Rashult, Sweden in 1707 and died in 1778 at the age of 70. He was a physician, botanist and zoologist. He is best known as father of modern taxonomy. He published his Syatma Naturae in the Netherlands. He collected and classifid numerous animals in 1750s. He laid down the nomenclature rules according to which man were classified as Homo sapiens.
3. Charles Robert Darwin: He was born in The Mount, Shrews bury and Shropshire, UK in 1809 and died in 1882. He is known worldwide for his book on the Origin of Species published in 4859. According to his theory, all species descended from a common ancestor, and evolution was the result of the natural selection. He studied marine invertebrates in preference to his original medical studies at the University of Edinburgh. His studies at the University of Cambridge notably influenced his trend and caused a vivid inclination towards natural science. It was during his five years voyage on the HMS Beagle that he convinced his remarkable Theory of Evolution.
4. Alfred Russel Wallace: He was born in UK in 1823 and died in 1931. He is famous for his independent theory of natural selection which prompted Charles Darwin to propound his Historical Theory of Evolution. He is considered as Father of of Bio-geography of the 19th century. He conducted intensive research in the Amazon River Basin and defined the Wallace Line according to which part of Indonesian archipelago had species of Indian origin. His another great contribution was, Wallace effect which hypothesised that the development of species was encouraged by the development of barriers against hybridization producing offspring by sexual reproduction.