This article contains spoilers from the most recent DCEU film. You have been warned.
At some point the sword was presumably created and wielded by the Olympian Goddess of Wisdom, Crafts, and Strategy, Athena.
Wonder Woman would eventually proceed to wield the sword against Doomsday, managing to slice off the monster's right arm with it.
The Sword of Athena is an incredibly sharp and durable weapon, showing no apparent damage after Diana's extensive use of it. It is likely also magical in nature, as are many Themysciran weapons, due to it's ability to injure otherwise invulnerable beings, like Superman and Doomsday.
It has an inscription carved in a form of Greek on the blade, which translates to English as follows: "Life is killing life all the time and so the goddess kills herself in sacrifice of her own animal".