Poseidon

One of the merman race who appear to be a homage of the monster from The Creature from the Black Lagoon. He is much bigger compared to humans and other mermen; his size can be compared to hills and buildings. He lost to Riza in a duel. In the manga he died after the duel but in the anime he is still living and fell in love with Riza. In the manga he was not given any name, but was named Poseidon in the anime.

(Source: Wikipedia)