The NKVD became the NKGB in 1941, the MGB in 1946, and then divided into 2 groups in 1954. The KGB was in charge of espionage, while the MVD was the secret police.
Oh, and today Russia's secret police are called the FSB.
So many initials. Boggles the mind. But when that knock came on the door, and the vehicle was waiting, it all boiled down to the same loss of freedom and of human rights ... interrogation and either death or the GULAG. (Those initials stood for: Glavnoe upravlenie lagerei - Main Camp Administration).