Vladimir Putin has fired the hardline adviser who directed the Kremlin campaign that fuelled separatism in Ukraine.
The dismissal of Vladislav Surkov was cautiously welcomed by officials in Ukraine hoping for a peace settlement.
His departure was first reported by an associate who announced he decided to resign because of "a change in policy toward Ukraine".
Mr Surkov curated the creation of two quasi-independent states in eastern Ukraine, propping them up with funds, weapons and troops.
He has been replaced by Dmitry Kozak, a veteran Kremlin insider largely seen as a moderate.