While DC's Superman was created during the Golden Age of Comics, he was not the most popular superhero of the era – and the true hero of the time outsold the Man of Steel so much that DC sued on his behalf. Very few Golden Age heroes of the late 30s and 40s remain active today, but occasionally some exceptions like Superman and Captain America can be found in the modern era. But Captain Marvel – now named Shazam – was the true champion of the 40s, and DC knew the only way to beat the character was to challenge him in court.

https://screenrant.com/shazam-captain-marvel-outsold-superman/