Needless to say, Xena: Warrior Princess is deeply engraved into Greek mythology. Numerous times Xena encounters mythical creatures and Greek gods. She battles some, befriends others, and is well known for her affair with the Greek god Ares However, there is a little bit more complication with the existence of gods in the Xena storyline.
The first non-Greek god that has a presence in Xena is the Judaic/Christian. His appearance reveals himself quiet early in the storyline, and there are one or two biblical stories that are also referenced. For example, the story of Abraham is told as a story arch; more subtly there is a mention about the 10 commandments at the end of an episode.
As the series progresses, so does the complexity of the gods. Midway through the series, there is a story arch in which a new god is begins to surface. This is where the complexity of the gods really beings. Did the god pre-exist and only began to gain power when the believers discovered his existence, or did he start to exist because the believers made him exist?
Even the after-life varies from different believers. Xena herself wandered two different after-death worlds. In both she was looking for two her friends who had died. Even though born Greek, the Amazon warriors have their own afterlife.
In its own way, Xena explains that the reason the Greek gods have no power today is because the people don't let them have power anymore. Within the show itself, you can see the gods beginning to worry when the threat of a new god arises. They worry that they will lose all their power with their people.