The Harpy Boss is an enemy of God of War that never made the final cut.
The general idea was that the "mama bird", which was the nickname given to the creature, would be encountered by Kratos while asleep, with Kratos having to steal her eggs and throw them in a fire, angering it. Kratos then would have to kill her so he could get to Pandora's Box, which she was guarding. This was introduced in the Deleted Levels documentary by David Jaffe, who considered the Harpy one of his favorites.