The Mythic Dawn was a secret cult that worshipped the Daedric Prince of Destruction, Mehrunes Dagon. The cult's existence can be traced back to the early days of Tiber Septim in the Second Era. The cult carried out an assassination plot against Emperor Uriel Septim VII and his heirs in 3E 433. Their deaths brought about the Oblivion Crisis, which resulted in a Daedric invasion of Tamriel and the end of the Third Era.
The Mythic Dawn was led by the "madman" Mankar Camoran, whose son Raven and daughter Ruma were his key lieutenants; all three were slain by the Champion of Cyrodiil. The Mythic Dawn had many sleeper agents posing as regular townsfolk scattered throughout Tamriel, as well as a shrine to Mehrunes Dagon hidden in a cavern near Lake Arrius that served as their base.
After the remnants of the Mythic Dawn were killed, Mehrunes Dagon's artifact, Mehrunes' Razor, was broken into three pieces. These pieces were hidden by several families, but were reunited in Skyrim during the Stormcloak Rebellion.