Akhundzada was a Taliban deputy leader and religious scholar who formerly ran the Taliban courts.
Mansour was killed in a drone strike on his car in Pakistan's Balochistan province on Saturday. Mansour was seen as obstacle to peace negotiations in Afghanistan and as a militant who only escalated attacks.
The rise of Mansour was seen by experts as something of a coup, which has since lead to heavy infighting between the group's factions. But Akhundzada carries with him largely religious credentials and was the man who issued fatwas justifying various operations.