Philip James Corso (May 22, 1915 – July 16, 1998) was a U.S. Army officer who served for 21 years in the military, rising to the rank of Lieutenant Colonel (some sources indicate Colonel). His decorated career included service in World War II, the Korean War, and a staff position on President Eisenhower's National Security Council from 1953 to 1957. He later served as Chief of the Foreign Technology Division in the Army's Research and Development department at the Pentagon from 1961 to 1963.

In 1997, one year before his death, Corso published The Day After Roswell (co-authored with William J. Birnes), in which he claimed that during his Pentagon tenure he had personally overseen a secret program to "seed" recovered Roswell crash debris into American industrial and defense research programs. He alleged that technologies including integrated circuits, fiber optics, night-vision equipment, and the kevlar vest had their origins in reverse-engineered alien materials.

Corso's claims are among the most dramatic and heavily disputed in the history of UFO research. Supporters point to his impressive military credentials, his sworn congressional testimony (he reportedly provided a signed affidavit to Senator Strom Thurmond for the book's foreword, though Thurmond later withdrew it after learning its content), and specific technical details he provided. Critics, including prominent historians and UFO researchers, have disputed key claims in the book, found inconsistencies in his account, and noted that the technologies he cited have well-documented conventional research origins.

Regardless of the verifiability of his claims, The Day After Roswell became one of the best-selling UFO books in history and significantly shaped public beliefs about Roswell and alleged government reverse-engineering programs.