Marcus Elieser Bloch (1723–1799) was a German medical doctor and naturalist.
Although he had limited education, he became a teacher in Hamburg, learned German and Latin and studied anatomy.
He later settled in Berlin where he became a physician.
Always interested in natural history, he amassed a private collection of natural objects.
He is generally considered one of the most important ichthyologists of the 18th century, and wrote many papers on natural history, comparative anatomy, and physiology.