Barry Kuda was from America. He and his pal Algie were sucked into a whirlpool, and dragged into the undersea kingdom of Merma. "Strange coral" there gave off "oxide" which replaced oxygen, allowing Barry and Algie to breathe underwater. He only had this ability if the oxide was in the water.
Barry and Algie help Queen Merma defend her home city of Merma from various invasion attempts. By the end of his stories, Barry wants to stay in the kingdom. Algie wants to go back to America, but continues to stay with Barry.
Throughout the series, Barry displays an ability to fight, and use weapons like swords, spears, clubs, and a "temperature equalizer" which could both freeze and burn.