The Elder Scrolls: Arena

The game's setting begins in Tamriel on the 389th year of the Third Era when Emperor Uriel Septim VII summons his advisor and Imperial Battlemage Jagar Tharn over concerns of betrayal from within the court. His concerns are justified when Tharn is revealed to be the traitor, magically trapping the Emperor and his general, Talin Warhaft, in another dimension.
When Tharn proceeds to magically disguise himself as Emperor to usurp the throne, his conspiracy is witnessed by mage apprentice Ria Silmane, whom he murders before she can warn the Elder Council. Tharn then summons demon minions to replace the Emperor's Guard. In his disguise, he sends the player character, a court official and subordinate of General Warhaft, to die in the Imperial dungeons.
After her death, Ria uses magic to take an incorporeal form. She holds herself together long enough to inform the imprisoned player of Tharn's betrayal and instructs them throughout their escape from the infamous dungeons. Past that point, she lacks the power to manifest physically and appears to the player during dreams. She creates a key to allow the player to escape the dungeons and teleports them to a different province through a mystical Shift Gate.
The player is informed that the only way to stop Tharn is to get hold of the Staff of Chaos, which holds his life force. Tharn has split this staff into many fragments throughout the continent of Tamriel. Each time one is found, Ria appears to the player the next time they rest to provide the general location of the next fragment. At the end of the quest in 3E 399 (a decade after the start of the game), the player finds the final piece and reassembles the staff. This, however, does not release the Emperor, as all of the staff's power has been drained into the Jewel of Fire, an oversight by Ria. The player travels to the Imperial City to confront Tharn's minions, the player finds the Jewel of Fire and touches it with the Staff of Chaos, this destroys both the jewel and the staff as well as releasing the Emperor. The jewel also turned out to be where Tharn had stored his life force, and the destruction of the jewel resulted in his death. As a token of respect and gratitude, Uriel Septim grants the player the title of Eternal Champion, and Ria Silmane finally enters the afterlife.