The Sword of El was a fabled weapon used by Von-El of the House of El.
After the end of the Age of Wars, Von-El thrown his sword into space to signified the end of all warfare between the people of Krypton, which was entrenched into Kryptonian legend. The Sword of El eventually landed on Krypton's sister planet Argo.
Many millennia later, Kryptonian archeologist Lin-El managed to pinpoint the sword's trajectory and managed to deduce where it had landed. Unfortunately, during one of his excavations an ancient, defective Eradicator buried underground was activated, and it eventually killed every inhabitant on the planet, except for Lin-El's step-daughter, Kara Zor-El who remained safely on suspended animation for the next decades, watched over by their robot assistant, Kurox.
After finally being rescued by Superman and his allies, Kara was finally able to finish her step-father's final work by unearthing the sword, which Superman proceded to activate to prove to her that he was a member of the House of El. Upon returning to Earth, the sword was kept inside the Fortress of Solitude in the hand of a memorial statue of Von-El.
Superman first used the sword in combat against Noram who had adquired possession of the Trident of Neptune. The sword proved superior than the trident, breaking off one of its points, and later Superman cut Noram's hand with it to fully disable him.
The Sword of El was forged to be a short-range and a long-range weapon. A monomolecular lash was built in the hilt, and a special gauntlet was crafted by Von-El to let him wield the lash in his free hand without being cut. Only Von-El and his blood descendants are capable of removing its sheath, making it one of the first protoypes in bio-coding of Kryptonian technology.
The Sword of El may have been based on the Sword of Superman from Superman Annual #10 (1984).