Stalin's successor was Khruschev, who dismantled Stalin's cult of personality, and reformed Stalin's system to an extent that Khruschev was removed from power without an incident by his own system, and lived happily ever after in retirement as the power transitioned to the next ruler.
Being the only ruler of Russia, over the past ~1000 or so years, to achieve that, namely:
1. Being removed from power (by term ending, elections lost, etc - not by their own will)
2. The removal happening procedurally, and not by disorder/coup/murder
3. Leaving the former ruler to live a decent life in retirement
Khruschev was a Ukrainian, see.