Isaak Konstantinovich Kikoin (Russian: Исаак Константинович Кикоин) (March 28, 1908, Žagarė, Lithuania, Russian Empire – December 28, 1984, Moscow, USSR) was a leading Soviet physicist and academician of the Academy of Sciences of the USSR. He was awarded the Stalin State Prize a total of four times (1942, 1949, 1951, 1953), the Lenin Prize in 1959, and the USSR State Prize in 1967 and 1980. Kikoin was named a Hero of Socialist Labor (1951); he also won the Kurchatov Medal (1971).
Kikoin was with Igor Kurchatov as one of the founders of the Kurchatov Atomic Energy Institute, which developed the first Soviet nuclear reactor in 1946. This was the lead-in to the Soviet atomic bomb project with the first atomic bomb test taking place in 1949.
In 1970, Kikoin (jointly with Andrey Kolmogorov) started issuing Kvant magazine, a popular science magazine in physics and mathematics for school students and teachers.