Different spellings of this last name are attributed to the different dialect pronunciations of people in different parts of ancient China. Common variations are: Chen, Tan, and Chan.


http://c.ancestry.com/i/search/nameorigin/gb_324.jpg: from name of the region of Chen (in present-day Henan province). After overthrowing the Shang dynasty and becoming the first king of the Zhou dynasty in 1122 bc, Wu Wang searched for a descendant of the great ancient emperors to guard their memory and offer sacrifices, to help retain the Mandate of Heaven, which was considered essential to remain in power. He found Gui Man, a descendant of the model emperor Shun (22572205 bc), and granted him the region of Chen, along with the title Marquis of Chen and one of his daughters in marriage. Gui Man was posthumously named Chen Hugong, and his descendants came to adopt the surname Chen.

Dictionary of American Family Names, Oxford University Press, ISBN 0-19-508137-4