The Sword of Ieldis is believed to be a Sith sword crafted by the Sith Lord known as Ieldis.
Prior to 3963 BBY, the Jedi Order placed the sword in quarantine on Coruscant. Investigations conducted by the Jedi Covenant indicated that the Helm of Dathka Graush, which is another Sith artifact, enhanced the sword's power.
Haazen attempted to wield the sword during the Vindication operation, not long before he died.