Nikolai Alexandrovitsch Gagen (Russian: Николай Александрович Гаген) (Lakhta, Saint Petersburg, March 12/24 1895 - Moscow, May 20, 1969) was a Soviet Lieutenant General in World War II.

Nikolai Gagen's ancestors were Baltic Germans which lived around Wenden in Livonia.

On April 28, 1943 he was promoted to Lieutenant General and was given command of the 57th Army, which he held until October 1944.

In January 1945, he returned to active service and was given command of the 26th Army deployed in southern Transdanubia, during the battle for Hungary.

He remained in this position until January 1959, when he was transferred to the reserve due to poor health.