Pieter Bleeker (July 10, 1819, Zaandam – January 24, 1878, The Hague) was a Dutch medical doctor, ichthyologist, famous for his work on the fish of East Asia – Atlas Ichthyologique des Orientales Neerlandaises – which was published 1862–1877, and herpetologist.
He was employed as a medical officer in the Dutch East Indian Army from 1842 to 1860, stationed in Indonesia. During that time, he did most of his ichthyology work, besides his duties in the army. Many of his specimens he got from local fishermen, but he also built up an extended network of contacts who would send him specimens from various government outposts throughout the islands. During his time in Indonesia, he collected well over 12,000 specimens, many of which are today at the Natural History Museum in Leiden.
Subsequent to his return to the Netherlands in 1860, he started publishing his Atlas Ichthyologique, a comprehensive account of his studies done in Indonesia with over 1,500 illustrations. It was published in 36 volumes between 1862 and Bleeker's death in 1878, and has been republished by the Smithsonian between 1977 and 1983 in 10 volumes.
Bleeker published more than 500 papers on ichthyology, describing 511 new genera and 1,925 new species.