In 1938, Action Comics #1 introduced the world to Superman, one of the first, and most enduring, superheroes to ever grace a comic book.
Since then, Superman has appeared in countless comic books, comic strips, movies, TV shows and video games. And one of his most defining features is the shield that adorns his barrel chest: the iconic "S." That "S" isn't just Superman's shield, though, it's also his logo, which has become so popular that people instantly recognize it as representing the Man of Steel.
What's most fascinating about that logo, though, is that at first, it wasn't really an important part of Superman's costume. It wasn't trademarked until 1945. Even before that, though, it was consistently changing to become the iconic logo recognized by people all over the world.
The Superman logo as most fans know it is usually a big red "S" sitting within a yellow shield. Not only did the "S" originally stand for "Superman," but it also represents "Saving Lives, Stopping Crime" and giving "Super Aid" when needed. It could potentially also represent Superman's creators, whose last names both started with an "S," Jerry Siegel and Joseph Shuster.
Superman's first "S" actually resembled a shield, with a big "S" in the middle. Although modern iterations of the logo insist that it is not an "S" at all, but the symbol of House Zor-El, it was definitely originally meant as an "S."
In Superman's first appearance in Action Comics #1, the shield resembles a police badge.
Eventually, though, the "S" symbol started changing and the police badge shape disappeared, replaced by a triangle, as in here, Action Comics #7:
Artists continued to tweak the colors and size of the "S" within the triangle, but this style remained fairly consistent. Sometimes the triangle was black, sometimes it was yellow. Once Superman had his own comic book series, the logo began to vary even more.
In 1944, though, the trademarked version of the logo appeared. It's similar to previous versions, but the triangle evolved into a five-sided shape. This set the standard for the logo as fans see it today. Here's Superman #26:
After the logo became trademarked, it remained consistent throughout Superman's illustrious career, although occasionally, artists like to go back to some of the original designs, honoring the shield's history.
Alex Ross's Superman #1 reverted back to the triangle shape:
Today's iteration of Superman, though, is classic: the red "S" on a yellow triangle encased in red. Here's the latest Superman in Action Comics: Rebirth #1:
Finally, here's an infographic showing how the logo changed, not just in comic books, but also in other media, as well.