Codex/Galactic History 52: Exar Kun Faces Korriban

The Galactic History 52: Exar Kun Faces Korriban codex entry is located within the Achievements:Datacrons section of a player's codex once it has been unlocked.

Codex entry
"This datacron holds unheard of power and knowledge collected by an ancient race. You access its power and discover writings which are clearly only one small piece of a massive galactic history:

Fascinated by tales of the ancient Sith and seeking greater knowledge, the Jedi Knight Exar Kun had defied his Master’s warnings and spoken with the spirit of Freedon Nadd on Dxun. On the Sith Lord’s advice, Exar Kun traveled to Korriban and began exploring its tombs. A cave-in soon pinned Exar Kun to the ground, nearly crushing him.

The spirit of Freedon Nadd spoke to Exar Kun again, promising he would rescue the young Jedi if he gave himself to the dark side. Still believing he was strong enough to resist the dark side’s lure, Exar Kun gave his word and power filled his body.

The cave-in was blasted away and Exar Kun’s injuries healed, but his promise had taken him much further into darkness. He left Korriban and, on Nadd’s advice, made his way to the forgotten world of Yavin Four."