Odin is a boss in Final Fantasy III. To challenge him, the party must obtain the Nautilus airship, and the enhancement that makes it into a submarine. The party can then enter the Saronia Catacombs by diving underwater.
After winning this battle, the player obtains Odin as a summon. In the 3D version, this is also the only opportunity to obtain the spear Gungnir, the most powerful weapon until the end of the game. The spear can be stolen by a Thief with a Job level of 71 or higher. The weapon also has a 0.3% chance of being dropped, allowing for a small chance to obtain two Gungnirs.
Odin uses his regular attack twice in one turn, which deals about 400 damage. His other move is Zantetsuken, known as Atom Edge in the NES version, which hits all party members for massive damage.