Committee for State Security (Russian: Комитет государственной безопасности) was a security agency in the Soviet Union, responsible for counter-intelligence, internal security and having some police features. KGB in some part was also responsible for foreign espionage.
The Cheka was the secret police of the USSR. Wikipedia maintains a list of the Cheka and its subsequent renamings:
1941: NKVD (again)
1943: NKGB ...
After the 1956 Hungarian upgrising, the KGB briefly deported Imre Nagy and his closest followers (Donáth, Lukács, etc.) to Romania. I understand that the Soviet Union would have wanted to remove Nagy ...