Danish archaeologist who deserves major credit for developing the three-part system of prehistory, naming the Stone, Bronze, and Iron ages for the successive stages of man's technological development in Europe. His tripartite scheme brought the first semblance of order to prehistory and formed the basis for chronological schemes developed for other areas of the globe by succeeding generations of archaeologists.

Curator of the National Museum of Denmark, Copenhagen (1816–65), Thomsen arrived at his nomenclature in the course of classifying and arranging the museum's large collection of Scandinavian antiquities. Based on 20 years of work, the scheme was published in Ledetraad til nordisk Oldkyndighed (1836; A Guide to Northern Antiquities). He also founded the first ethnographic museum.