At a specific point in Assassin’s Creed Odyssey, you’ll come across a nasty group of people that call themselves the Cult of Kosmos. Their collective goal is to bend the world to their whims by prolonging the Peloponnesian war, terrorising the local populace, and causing widespread chaos.
Assassinating them all becomes one of Alexios or Kassandra’s main focuses of their odyssey. To work out who the major players are and where to find them, you need to kill their subordinates and gather clues that lead you to the sages, and their leader.