Meranno is a member of th aquatic rce of being s know as Homo Mermanus. As a boy Meranno was a playmate of Prince Namor, the Sub-Mariner
, but actually despised him. In the late 1930s Meranno worked as a research scientist in the Atlanteans' Antarctic city. Allying himself with Nazi Germany, Meranno betrayed the city's location to the Nazis, who launched an attack that severely damaged the Atlantean fleet, destroyed the Atlantean Hall of Science,and left Atlantis's Emperor Thakorr
in a coma. Namor, as acting Emperor, banished Meranno for treason. Meranno then joined the Nazis in their mad quest for world domination, expecting a Nazi Victoryto bring him enough personal power to wreak his vengenace against Namor. using a combination of his own advanced Atlantean scientific knowledge and Nazi science, he developed an as-yet-unknown means of increasing his size and strenght to a point where he rivaled the Sub-Mariner himself for might. Dubbing himself U-Man, Meranno Went on to fight alongside the Axis in World War II, often coming into confilict with his hated enemy Namor and Namor's allies, the small band of adventures known as the Invaders
. In the end, however, Meranno found himself defeated time and again, encountering the final end to his plans of vengeance with the defeat of Germany in 1945, although he was never capture and tried as a war criminal.
Although today Meranno would be aged by human standard, Atlanteans enjoy a lifespan consdierably longer than that of surface men; therefore, Meranno is considered to be in the prime of his life by Atlantean standards. Recently, Merparticipate din the Atlantean warlord Attuma
's failed atempt to conquer the surface world. His current whereabouts are unknown.