The first decade or so after Superman was introduced in 1938 is generally known today as the "Golden Age" of comics, particularly when it comes to superhero books. The fascinating dichotomy present in this era is that it is remembered so fondly (hence the "Golden Age" moniker) while it was also when comic books were at their most disposable. During this era, comic books were produced in the millions but were treated like junk. World War II, in particular, drove a desire for escapist fare and the troops at home and abroad were some of the biggest purchasers of superhero comic books at the time. Since the demand was so high, comic books were thrown together quite haphazardly. There are more than a few examples of a comic book company getting a hold of a batch of paper, which was hard to come by at the time, and then quickly putting out an entire comic book in a weekend just to take advantage of the availability of the paper.
This disposability was reflected in the characters themselves. Since the writers of the comics did not expect anyone to remember any given story, they were all over the place in terms of consistency. Characters saw their power levels grow and grow as the writers would simply have them come up with new powers to deal with whatever situation presented itself. As a result, Golden Age superheroes are some of the most powerful superheroes ever, especially compared to their modern day equivalents. Note that some of these "equivalents" are literally just in name only (like Green Lantern Alan Scott compared to Green Lantern Hal Jordan).
The main example of the trend towards over-powering superheroes during the Golden Age has to be Superman. When he was originally introduced, Superman was noted as being "more powerful than a locomotive" and "able to leap tall buildings in a single bound." While that was certainly very impressive back in 1938, within a few years those feats would seem like minor pittances.
Soon, the Man of Steel was flying and lifting entire planets as if it was no big deal. These extraordinary feats have led to a number of reductions in Superman's strength over the years. This took place first in the early 1970s and then more significantly following Crisis on Infinite Earths in 1986.
19 CAPTAIN MARVEL
Superman's greatest superhero rival during the 1940s was Captain Marvel, Earth's Mightiest Mortal. Clearly intended to be a riff on Superman, only with a magical element mixed in there, Captain Marvel was outselling all superheroes, the Man of Steel included, by 1944. Just like Superman, Captain Marvel's powers seemed to grow whenever a writer needed him to be able to do something extraordinary.
National Comics (now DC Comics) had been in court with Fawcett Comics for over a decade in its attempts to claim that Captain Marvel was infringing on National's Superman copyright. Eventually, Fawcett gave up and years later, sold the character to DC Comics. Now dubbed Shazam, his powers are a good deal weaker than they were in the 1940s.
Jerry Siegel did a lot more than just co-create Superman. With Bernard Baily, he introduced the grim spirit of vengeance known as the Spectre, in 1940. The Spectre could seemingly do anything it wanted in terms of punishing bad guys.
That original take on the Spectre was brought back briefly in the early 1970s when DC Editor Joe Orlando was mugged and he began to think of what he would have liked to have seen happen to those muggers. In more recent years, the Spectre has become a bit more tangled up in various DC storylines and his power levels are a bit inconsistent. Sometimes he is as powerful as ever and sometimes he is restrained.
17 BLUE BEETLE
One of the most notable examples of the "power creep" that occurred with many Golden Age superheroes was what happened to the Blue Beetle in the 1940s. Introduced as a hero who just fought crime with his wits and fists alone, Blue Beetle then gained a special bulletproof costume. This costume slowly also gave him super-strength, as well.
As the decade went by, though, Blue Beetle developed X-Ray vision and even more powers that came and went as the writers thought of them. The current Blue Beetle, Jaime Reyes, is strong as well, but the original Blue Beetle had become way overpowered by the end of the 1940s.
16 CAPTAIN MARVEL JR.
An area where Fawcett beat National Comics to the punch was that the company came up with the idea of spin-off characters first. A number of years before Superboy first debuted, Fawcett introduced Captain Marvel Jr., a younger version of Captain Marvel. The character had the same basic set-up of Captain Marvel, where a boy shouts a magic word and transforms into a mighty being. This time, though, the transformation kept Freddy Freeman the same age as he was before he shouted the magic word!
Captain Marvel Jr. had all of Captain Marvel's powers, which meant that he was pulling off feats like moving the planet Mars to avoid some deadly gases escaping that would affect Earth.
It might have taken a while, but eventually National Comics did introduce a younger version of Superman known as Superboy. Jerry Siegel and Joe Shuster originated the character, but National took him in a different direction than where Siegel intended. Superman's co-creator wanted Superboy to be essentially a super-powered prankster. In the actual comics, though, Superboy was just like Superman only younger.
His adventures took place in Smallville, where Clark Kent grew up. However, since he was a younger version of the Man of Steel, Superboy's feats of strength soon hit to planet-moving levels, as well. The modern version of Superboy doesn't even come close, power-wise.
In 1968, Stan Lee told Roy Thomas that he wanted him to add a new member to the Avengers. Roy Thomas had just the guy in mind, the overlooked Golden Age superhero known as the Vision. Lee told him no, he wanted Thomas to introduce a new character and that he had to make him an android, as well. So Thomas just introduced a new android version of the Vision.
The original Vision, though, was an extremely powerful alien from another dimension who had a variety of powers. The modern Vision is a powerhouse in his own right, of course, but the alien Vision is probably slightly stronger.
13 WONDER MAN
As soon as Superman was introduced in Action Comics #1, he was a sales sensation. You better believe that the other comic book publishers were paying attention. In fact, whole new comic book companies were formed just to try to come up with their own version of Superman. One of these companies, Fox Publications, came a little too close with its character Wonder Man. National Comics sued the company and it had to drop the character.
Decades later, Marvel introduced its own Wonder Man, and while the Marvel Wonder Man had fists that hit like Thor's hammer, that is still not as powerful as the original character, who was essentially just Superman under a different name.
12 GREEN LANTERN
Grant Morrison recently announced that he will be relaunching Green Lantern for DC Comics, and his take on the book sounds a whole lot like the original one on Green Lantern back when Alan Scott was the hero who was wielding the jade piece of jewelry. Morrison has even been describing Hal Jordan's power ring as a "magic wishing ring."
That basically was how Alan Scott's ring worked during the Golden Age, and while Hal Jordan's Guardians of the Universe-supplied ring was certainly very powerful, it seemed like Alan Scott's ring had no limitations at all outside of its weakness to wood (like Hal Jordan's ring's weakness to yellow).
11 MARY MARVEL
Following the success of Captain Marvel Jr., Fawcett decided to double down on Captain Marvel spin-off characters and introduced Mary Marvel. It turned out that Billy Batson had a twin sister that he didn't know about who had been adopted by a family. Reunited, Mary discovers that she can share Billy's power and transform into Mary Marvel.
Generally speaking, Mary Marvel was shown to be slightly weaker than the other members of the Marvel Family, but she still pulled off a number of planet-moving level feats. The modern version of Mary Marvel is not even close to the same power level.
10 DOCTOR FATE
One of the trickier examples on this list is Doctor Fate, because it really depends on what version is currently the one at play in the modern DC Universe. The Golden Age Doctor Fate is an easy guy to describe, as he was practically all-powerful. He was on par with the Spectre in terms of seemingly unlimited power. Whatever he wanted to do, he could do.
That is not that far off from some modern versions of Doctor Fate, but the most recent Fate to have his own series, Khalid Nassour, had a lot more trouble getting use to his role as one of the most powerful magical beings in the DC Universe, so he is noticeably weaker than the Golden Age Doctor Fate.
Another excellent example of the haphazard nature of Golden Age comic book plotting is the original Atom. When he was introduced, Al Pratt's deal was that he was really short but he was very strong for his size. So he took people by surprise when they would underestimate him for being so small. He had no superpowers at all, though. He was just a good fighter.
Well, out of nowhere, in 1948, he suddenly had a new costume and super-strength! There was no explanation, he just had superpowers out of nowhere. The modern Atom also has superpowers, but they are not strength-based (he can shrink himself), so the Golden Age version would take the cake in that category.
8 KID ETERNITY
The original Kid Eternity was a young boy who was on his grandfather's fishing boat when it was sunk by a U-Boat during World War II. This was a screw-up, as he was not supposed to pass on for another 75 years. So he was sent back to Earth, only now he had the ability to call forth any mythological or historical figure or animal whenever he wanted by shouting the magic word, "Eternity!"
The modern version of Kid Eternity had similar powers, but they were a lot more limited. He could only call a single spirit for roughly a minute. So the Golden Age version was a lot more powerful.
7 THE RAY
The Golden Age Ray has generally the same powers as every other version of the superhero. He can transform himself into light and has control over his light beams, as well. However, the big different between the modern versions of the Ray and the original one is something that we alluded to earlier. In the Golden Age, characters would just gain powers out of nowhere.
So the original Ray did not just have all of the classic powers of the Ray, but he would also be able to control magnetism, he had super strength at times and he could control electricity.
6 UNCLE SAM
Another excellent example of a character whose powers fluctuated depending on the story that he was appearing in at the time was Uncle Sam, a patriotic superhero that Will Eisner created for Quality Comics in 1940. Uncle Sam was a Revolutionary War soldier who perished during battle and was brought back as a powerful spirit who was powered by the spirit of the United States itself.
The Golden Age version of the character could grow to giant size, had super strength and could even travel through dimensions. Later versions of the character were still strong, but not nearly at the same level.
5 BLACK WIDOW
The modern day Black Widow is a skilled fighter and a brilliant espionage agent who arms herself with a powerful blaster known as the "Widow's Bite." She is a formidable foe, but decades before she debuted, Marvel had a whole other Black Widow character back when it was known as Timely Comics. This Black Widow was in a whole other world from her modern-day counterpart.
The Golden Age Black Widow cut a deal with the devil where she would bring souls to the netherworld. She gained a variety of magical powers to help her in her quest, including flight, invisibility and, of course, super-strength.
4 BLAZING SKULL
Mark Todd was a foreign correspondent in the years leading up to World War II. While covering the war between Japan and China, Todd accidentally uncovered an ancient race of people known as the Skull Men. They decided that Todd would be their new representative in the world to fight for freedom using the abilities that they gave him.
He trained with them before going off into the world as the Blazing Skull. He was invulnerable to fire, was able to turn his skin invisible so that just his skull would be visible and he had super strength. The later Marvel hero, Skull the Slayer, briefly took over as the Blazing Skull, only without nearly the same level of powers.
3 HUMAN TORCH
When Martin Goodman told Stan Lee to introduce a new superhero team to compete with DC Comics' then-new hit comic book series, Justice League of America, Goodman wanted Lee to use some of Marvel's old Golden Age characters. Lee wanted to use brand-new characters but their compromise was that Lee and Jack Kirby would include a new version of the Golden Age hero, the Human Torch, as part of the Fantastic Four.
Johnny Storm had most of the same abilities as the android hero from the Golden Age, but the original Human Torch also had the ability to survive being at the middle of the detonation of a nuclear bomb, so we're going to say the original Torch was just a hair stronger.
2 MARVEL BOY
When it comes to characters sharing the same name, few superhero names have had as many different versions as Marvel Boy. There was a 1950 version of the character that later became a member of the Agents of Atlas, but we are looking at the first one that Timely Comics introduced. This Marvel Boy had the powers of Hercules reincarnated.
That makes him stronger than the 1990s version of Marvel Boy, who was a member of the New Warriors for years. There was an alien version of Marvel Boy, known as Noh-Varr, that might be as strong as Hercules, but we will still give the strength nod to the original version.
1 BULLETMAN AND BULLETGIRL
Golden Age comic book superheroes often had some wild origins. Few of them were quite as odd as Bulletman, who invented a special helmet that looked like, well, a bullet and that would give its wearer super-strength and the ability to fly. He later made a similar helmet for his girlfriend (later wife) and they became the superhero duo known as Bulletman and Bulletgirl.
Years later, Grant Morrison did an event called Seven Soldiers where he revamped a number of classic superhero concepts. One of his ideas was Bulleteer, a woman who was coated with an unbreakable metal later, making her sort of a living bullet. She did not have the strength levels of the original Bulletman and Bulletgirl, however.