Manno the Mer-Man... an oft-forgotten footnote in the history of Wonder Woman. Residing in an unknown
part of the Atlantic Ocean, perhaps connected with Tritonis where Lori Lemaris originated... Manno first made his appearance known to the surface world as Mer-Boy with the alternate name of Ronno. It was on his first trip above the waves the he fell in love with the young Princess Diana, affectionately known to her fellow Amazonians as Wonder Girl. The pair had an on-again off-again courtship that precipitated into some startling adventures with one another. Years later, the now adult Diana as the superheroine known as Wonder Woman would fall in love with American Colonel Steve Trevor, although Trevor would find intense competition from Mer-Man who reappeared in his childhood sweetheart's life once more. Then, through a series of Impossible Tales which were tangentially tied to Earth-One's continuity, Mer-Man would be aided by his younger selves of Mer-Mite and Mer-Boy to aid Wonder Woman with her younger selves of Wonder-Mite and Wonder Girl. Within a couple years of his reappearance, Mer-Man would return to his life in the sea forsaking any future hope of ending up with the Amazing Amazon.
On Earth-Two, the golden age Wonder Woman had far worse experiences with her world's Mer-Men who were ancient adversaries of the Amazons. On one occasion, they kidnapped the Queen of Paradise Island which led to Princess Diana nearly becoming the new Queen, until she was able to track down her mother's kidnappers. This was the sole recorded meeting between Wonder Woman and her Mer-Men, however given her reference to past encounters with this troublesome race tempered by some bitter feelings she had for them, its obvious that some tales haven't yet been chronicled of these undersea dwellers. Besides being a more aggressive race than were those on Earth-One, the Earth-Two Mer-Men possessed two fish tales to compensate for two legs of humans whereas their counterparts possessed only one combined fish tale.