In the original God of War, the goddess Artemis grants Kratos the Blade of Artemis.
The Blade of Artemis is an optional magical weapon that Kratos can obtain during his quest to defeat Ares. It is a large curved sword associated with Artemis, the Greek goddess of the hunt. The weapon provides a different fighting style from the chained Blades of Chaos.
In the 2005 game, players spend red orbs to upgrade weapons and magical abilities. The Blade of Artemis is therefore part of the original game's broader equipment system, which lets Kratos expand his attack options as the adventure progresses.
Artemis is not the same character as Athena, who plays a major guiding role in the series. The Blades of Chaos are also separate: they are Kratos's signature chained weapons and were given to him by Ares.