Perseus was the codename of a possible Soviet spy alleged to have breached U.S. national security at Los Alamos during the Manhattan project. This name is also given to a spy at White Sands Missile Range, located further south near Las Cruces, New Mexico. Evidence for his or her existence is based on a few references in KGB archives opened (and later closed) to researchers in the early 1990s, after the fall of the Soviet Union. There are also a few references to Perseus in the VENONA decrypts as PERS. The identity of this person, or even whether or not they actually existed, is unknown, and many of the facts in the matter are questionable.
The first person to publicly write about atomic spy Perseus was Russian intelligence Colonel Vladimir Chikov. Starting in 1991 he wrote a number of articles in Russian periodicals that discussed Perseus. Later in 1996 he published a book with American co-author Gary Kern titled, How Stalin Stole the Atomic Bomb from the Americans (published in France in French).
US Cold War historian John Earl Haynes believes that Perseus is "a faked composite by Vladimir Chikov and the SVR combining part of the story of Theodore Hall with misdirection and distortion"[1] citing Gary Kern[2]
The Venona messages contain the unidentified codename "PERS." Not only is pers the linguistic root of the word Perseus but the messages suggest that PERS was a Soviet source on the Manhattan Project. In addition to this, many other individuals, including some associated with the KGB, have affirmed either the specific existence of Perseus or that there remain unidentified atomic spies on the Manhattan Project. According to Chikov, Perseus was at Los Alamos in 1943, a year before Fuchs was assigned there, and in the 1950s Perseus was under the control of Rudolf Abel.