Out of all of Marvel's Golden Age heroes, Namor was definitely the most morally ambiguous. At any moment, the Sub-Mariner could be a hero, a villain or anything in-between. Namor's dubious morality led to Marvel's first major crisis when he flooded much of the world in the 1940s.. Ever since his first appearance in 1939's Marvel Comics #1, in a tale by Bill Everett, Namor acted as a sort of anti-hero. The Sub-Mariner devoted his life to a war against the surface world, on behalf of his kingdom of Atlantis. At the same time, Namor would occasionally side with some of the Earth's surface-dwellers to fight the Nazis during World War II.
In 1940's Marvel Mystery Comics #8, by Bill Everett and Carl Burgos, Namor also met the original Human Torch, resulting in Marvel's first superhero battle. Of course, soon afterwards, Namor and the Human Torch would become uneasy allies, fighting side by side against the Nazis. All of these conflicting events contributed to Namor's morally unclear role in the early Marvel Universe.
It wasn't until 1941's Human Torch #5, by Carl Burgos, Henry P. Chapman, Jack D'Arcy, Bill Everett, George Kapitan, Mike Roy and Harry Sahle that Namor truly showed his villainous potential. During this issue, the Atlanteans expressed how the ongoing war among the surface dwellers had caused problems for their kingdom. An Atlantean named Rathia convinced Namor to wage war on the surface world, appealing to his ego and manipulating him into doing her bidding. The Sub-Mariner took the fight to every major nation in the world, causing serious damage. Along the way, Namor also fought the Human Torch and his sidekick, Toro. Eventually, Namor realized the horror which he'd caused, joining up with the Human Torch to stop Rathia. Despite his change of heart, Namor had still done some serious damage. Most memorably, Namor flooded New York City, an act which would live in infamy as Marvel's first major crisis.
Namor's attack on the surface world was retold as a major catastrophe in the pages of 1994's Marvels #1, by Kurt Busiek and Alex Ross. From the perspective of Phil Sheldon, a local reporter, Namor's attack came as a shock. Many people at the time of the attack were confused, as they thought the Sub-Mariner was on the side of the Allies during World War II. Revisiting Marvel's history, this tale revealed the panic and drama which ensued when everyone heard that Namor was attacking New York. Evacuations were underway and people around the city were sent to shelters so they could be safe from Namor's impending assault. This assault was essentially treated as a natural disaster, for which citizens would have to brace themselves. One double-page spread, highlighting the tidal wave which hit New York, emphasized the severity of Namor's attack on the city. Namor's impact on the average New Yorker was made very clear, making his attack bad enough.
Even worse, however, was the sense of confusion when Sheldon heard that Namor had returned to the side of good. After destroying much of New York, somehow Namor was welcomed back on the side of the heroes. This says a lot about Namor's ambiguous morality, showing how he could either be mankind's best friend or worst enemy at any moment. 2010's The Marvels Project #6, by Ed Brubaker and Steve Epting also emphasized the severity of Namor's attack. In the pages of this issue, countless lives were lost in the flood, as New Yorkers were swept up by Namor's tremendous power. Once again, Namor's attack was shown as a devastating event for Marvel's ordinary citizens.
A big rescue effort was shown as well, highlighting how Namor's attack brought all of Marvel's Golden Age heroes together to save lives. Even Captain America arrived to fight Namor alongside the Human Torch. Demonstrating both the massive loss of life and destruction of property, The Marvels Project emphasized that Namor truly caused Marvel's first major crisis. Only a devastating attack of this scale would bring all of Marvel's heroes together. In both Marvels and The Marvels Project, Namor's attack was shown to have a major impact on everyday citizens. In this way, Namor showed the serious consequences of major Marvel events on those the heroes would save. Despite his innate nobility, Namor was still the first to cause a major Marvel crisis.