One of the most interesting recurring enemy characters in Final Fantasy VI is the purple octopus Ultros, known as Orthros in the Japanese version. Since Orthros is a two-headed dog from Greek mythology, I couldn't really say why the designers would think it an appropriate name for a sea monster. Oh, well. Ultros shows up to fight the heroes four times during the course of FF6, and doesn't appear to have any loyalty to the Empire or anyone else. He's just a hungry, sass-mouthed nuisance. He's generally played as comic relief, and makes a lot of quips both in the battle and out of it.
He first shows up to fight on the River Lethe, and next at the opera house, where he plans to drop a heavy weight on the star of the show.
Interestingly, his dialogue in this scene includes, "You've changed! Did you miss me?", despite the fact that it's entirely possible you're fighting him with entirely different characters. The group fighting Ultros on the first encounter consists of Terra, Banon, Edgar, and Sabin. During the opera scene, Terra is out of commission and Banon no longer playable. Edgar and/or Sabin could be in your party, but neither one is required. The third fight occurs in the Esper Cave, where the octopus tries to steal three golden statues, claiming it will make Siegfried jealous. Siegfried's role in this game is mysterious, so how he knows Ultros and why he'd be jealous of the statues is never explained. I think his story might be best saved for another post, though. This time, he runs off when Relm paints his picture, proving how ugly he is.
The final Ultros battle is on the airship, proving that the sea creature is somehow equally at home in the sky. This time, he brings along his partner Chupon, who in Japanese was known as Typhon, after the wind god. According to his Final Fantasy Wiki page, "Chupón" is Spanish for "sucker," so I guess the English translator wanted to work in an extra joke.
Chupon's specialty is sneezing, which he uses to blow the party off the ship. Both of these villains reappear in the Colosseum in the second part of the game. Ultros is working as a receptionist, and Chupon fights anyone who wagers a common item.
I'm apparently not the only one who found Ultros to be a memorable character. The octopus made cameo appearances in several other games, and I recently came across this Japanese pop song about him. Oddly, it uses both his English and Japanese names, but I guess that's pretty common for Japanese lyrics.