Ronno (Manno) is a merman in a DC Comics Universe. He used aliases Mer-Mite, Mer-Boy and Mer-Man throughout his different ages.
During the Silver Age of comic books (the 50's and 60's), teenaged Wonder Woman (then known as Wonder Girl) had two suitors: Mer-Boy and Bird-Boy. Mer-Boy grew up and became a rival for Steve Trevor for Wonder Woman's affection. Ronno and Wonder Woman had adventures together with their younger selves.
He shows great skill and talent in wrangling sea creatures and fighting underwater, but is very awkward on land, as he has no legs and can only hop around on his tail fin. Due to his clumsiness, he frequently ends up in trouble, necessitating Wonder Woman to rescue him.