Odin

Odin, previously known as Gold (born Ethan) is the leader of Team Asgard in Pokémon Zeta.

The first time you meet him is in the museum in Onega Town when he steals the Time Caller and then catches Shaymin. The first time you battle him, he is on Mt. Press where he tries to catch Jirachi.

Nyasa Town
Immediately after defeating the Champion of the elite four you go to Nyasa Town where Odin challenges you once again. This time it's tough since he has a new legendary and you are worn out after the elite four. If you lose the story progresses anyway.

Varlox Cave
Odin is one of the people you have to defeat in Varlox Cave. He challenges you immediately after you've battled Red.