Another atomic spy is revealed

This one is pretty important:

George Koval also had a secret. During World War II, he was a top Soviet spy, code named Delmar and trained by Stalin’s ruthless bureau of military intelligence.

Atomic spies are old stuff. But historians say Dr. Koval, who died in his 90s last year in Moscow and whose name is just coming to light publicly, was probably one of the most important spies of the 20th century.