Perseus was the code name for a scientist who passed secrets to the communist Soviet Union beginning in 1943 in Los Alamos on the Manhattan Project, before the acknowledged spy Klaus Fuchs arrived, and continuing into the 1950s. In 1996 Vladimir Chikov and Gary Kern published the book, Comment Staline a vole la bombe atomique aux Americains, Dossier KGB No. 13676 (How Stalin stole the atomic bomb from the Americans, File No. 13676, The Case of the Cottagers).  It is the story of Morris and Lona Cohen, an American couple who were Soviet espionage agents. More particularly, it is the story of Morris Cohen's recruitment in 1942 of an atomic physicist employed by the Manhattan Project. Chikov does not identify the physicist, initially using the alias "Arthur Fielding" to refer to him. At the point in the story when Fielding is transferred to Los Alamos--1943--Chikov gives him the spy name Perseus. However, Chikov stated that Perseus was not fictitious; that, in fact, it was a field name (cover name) actually used by the Cohens and their Soviet controller to refer to their prodigious source working at the heart of "Gorgon," the bomb.
The Chikov-Kern collaboration began in 1993, and the manuscript was largely completed by mid-1995. At the time of writing Vladimir Chikov was a Lt. Colonel press officer with the Russian Foreign Intelligence Service (SVR) intelligence service, formerly the KGB. Kern, who studied at Princeton, is a widely acclaimed Russian translator and sovietologist. The Preface of the book was written by Robert Lamphere, FBI liaison to the Venona Project, head of the SOVME Unit and later supervisor of the Rosenberg Case.
Chikov’s account was released with the cooperation of the Russian successor agency to the KGB and the information he gives must be evaluated with that in mind. Because the SVR still has institutional reasons to maintain the secrecy of Soviet-era spies, Chikov gives a pseudonym for the scientist Cohen/Louis recruited. Out of a desire to obscure exactly who was recruited, we regard it as possible that the date Chikov gives is not exact.  Chikov's earliest writing about the Cohens' involvement in atomic espionage was a magazine article in New Times (Novoye Vremya) in April 1991. A number of elements from that account are incorporated in this set--they differ from Comment Staline, but may be closer to the truth.
Almost all commentators agree that Vladimir Chikov constructed his Perseus legend from the espionage activities of two or more KGB sources on the Manhattan Project. Based on the above conflation, an alternative profile for Perseus might be: a Manhattan Project physicist who was acquainted with Steve Nelson; who was an associate of Robert Oppenheimer; who worked at the Met Lab in 1942; and whose career reflects employment in the Philadelphia area in mid-1944.
In The Theory of Fielding, H. Laes concludes,
- "J. Robert Oppenheimer was an agent of the Soviet Union. He was not Perseus, the spy alleged by Chikov. However, he was the witting enabler of Perseus and other spies." 
- Los Alamos National Laboratories History:Spies. Retrieved from lanl.gov 14 July 2007.
- Carley v. Klehr & Haynes:Secret World of American Communism, 6 July 1995. Retrieved from H-Net 14 July 2007.
- Theory of Fielding - Conclusion - Perseus, H. B. Laes.