Time travel has been a story element in DC Comics since 1935's "The Magical Crystal of History" by Alphonse Barreaux in New Fun Comics #1. Since that early story, many creators used the plot device for generic comedy or adventure tales. It was not until 1942 that costumed heroes traveled through time. After that, time became a location for super-adventurers to explore.
Because time travel messes up cause and effect, date of publication is the only real way to consider which characters broke the time barrier first. Anytime someone tries explaining the paradoxes of time travel, it makes brains crack and eyes cross. It's best to remember that these are comic book stories and just enjoy the ride.
10 Captain Marvel Helped Doctor Sivana Build A Time Machine
Whiz Comics #26, January 1942
In the 1940s, DC Comics saw real competition from Fawcett Comics and the original Captain Marvel, now known as Shazam. DC purchased Fawcett in the 1970s, along with Captain Marvel and all their other heroes. DC quickly incorporated them into their lineup of heroes and villains accordingly.
The Big Red Cheese's first experience in time travel came in January 1942's WHIZ Comics #26 by C.C. Beck. The hero went to Dr. Vanna's laboratory and the two built a time machine together. Dr. Vanna fell into the time machine and emerged as Marvel's nemesis, Doctor Sivana, who successfully tricked the hero into a journey to prehistoric times before a time traveler from 6942 helped Billy find his way home.
9 The Flash Jay Garrick Used Pills To Travel In Time
All Flash #4, March 1942
The original Flash, Jay Garrick's first trip in time wasn't fueled by his fantastic speed but by pills made by Professor Archibald McQuatness. It went down in March 1942's All Flash #4 by Gardner Fox and E.E. Hibbard. McQuatness traveled back 2,000 years to witness Flash burying a time capsule. His backer, the crooked Reginald Hasto, tried to kill the professor and steal the buried treasure.
The Flash intervened, and the ensuing adventure took place in Ancient Rome, where the speedster earned a reward for saving Julius Caesar. By the end, Hasto tripped into his own death trap, dying over nothing since the time capsule was empty from the start.
8 Seven Soldiers Of Victory Visited Troy With Dr. Doome's Time Machine
Leading Comics #3, June 1942
It feels odd, knowing that Green Arrow traveled through time before Batman or Superman. However, in June 1942's Leading Comics #3, the archer was among the Seven Soldiers of Victory when they pursued the evil scientist Dr. Doome into the past. Yes, twenty years before Marvel's Doctor Doom, DC had a villain named Dr. Doome with a time machine.
Doome brought historical villains like Napoleon and Genghis Khan through time to steal for him, prompting the Soldiers split up to thwart them. They regrouped to confront Doome only to have him flee into the past, where they pursued him to the end of the Trojan War. The story ended with Doome's machine exploding, trapping the villain in the distant future.
7 Mr. Terrific Was Summoned To Save Future Earth
Sensation Comics #28, April 1944
The much less-famous Golden Age Mr. Terrific time-traveled before any of DC Comics' big three heroes, making his first journey in April of 1944. In this tale, he was summoned to the year 7532 to rescue an influential scientist called the Coordinator after he was kidnapped by would-be tyrant Black Barax.
The adventure showed how Golden Age writers incorporated solid logic into their time travel stories. The Coordinator's unique function was stabilizing Earth's orbit after a rogue planet entered the solar system. Rogue planets were a suspected cosmic threat in the 1940s and Edwin Balmer and Philip Wylie depicted this scenario in their 1934 novel When Worlds Collide. Mr. Terrific was able to save the future Earth and apprehend the thugs he was fighting in 1944 by having the future scientists return him to the exact moment he vanished from.
6 Midnight Also Used Pills To Time Travel
Smash Comics #52, April 1944
Looking like a photocopy of Will Eisner's The Spirit wasn't enough for Midnight. He also stole a page from the Flash's book by using pills to journey through time. This happened when Midnight's Gyro Gearloose equivalent, Doc Wackey, created a batch of time travel pills.
A careless thought sent the group to Nero's Rome. Attacked by Roman soldiers, they're taken before Nero. Midnight led their escape but ended up burning down Rome's capital. Doc Wackey returned the group to the present, leaving Nero to take the blame for the great fire.
5 Wonder Woman Accidentally Traveled Through Time
Wonder Woman #9, June 1944
In Wonder Woman #9, William Moulton Marston and Harry G. Peter told the story of Professor Zool's Evolutionizer. The Professor first used the machine to evolve a gorilla named Giganta into a woman. When Giganta attacked Wonder Woman, it damaged the machine and sent everyone in the vicinity back to prehistoric times.
In a confusing development, the human characters also devolved into primitive forms. However, Giganta actually saved the day when she discovered that Wonder Woman's magic lasso could serve as a power source for the machine. It was one of the more chaotic forays into time travel in early DC history.
4 Batman and Robin Sent Their Minds Back To Ancient Rome
Batman #24, August 1944
In the Golden Age, Batman and Robin had an ally who developed two methods of time travel. Before Professor Carter Nichols built a physical time machine, he developed a means of psychically sending a person into the past. Batman and Robin used this method on their first journey through time in August 1944.
The adventure saw Professor Nichols send Bruce Wayne and Dick Grayson back to ancient Rome where the heroes donned their costumes to thwart a nefarious plot. However, Nichols assumed his experiment failed because the two mumbled about Batman and Robin while they were under hypnosis.
3 Green Lantern Went To The Legendary Camelot
All-American Comics #72, April 1946
In All-American Comics #72, Alfred Bester and Paul Reinman sent Green Lantern Alan Scott into the past. Here, Merlin summoned Green Lantern and his sidekick Doiby Dickles to Camelot to aid King Arthur, who needed help vanquishing a dragon and finding a missing Chinese delegation.
In a confusing twist, the dragon turned out to be Roger Bacon perfecting his formula for gunpowder in seclusion. Green Lantern used the explosive to defeat an evil knight and save the Chinese delegation. Fortunately, the delegation happened to have Scott's lantern with them, so he was able to charge up his ring and return home.
2 Mary Marvel and Captain Marvel Jr. Pursued Sivana's Children Through Time
Marvel Family #10, April 1947
Marvel Family #10, by Otto Binder, C.C. Beck, Pete Costanza, Jack Binder, and Bud Thompson, featured the Marvels following the evil super-scientist Sivana family through time. Mary Marvel and Captain Marvel, Jr. got into trouble when the Sivanas cut them off from the mystical power source. However, they were able to wreck the machine sabotaging their powers and save the day.
Per usual, the Marvel Family was able to make short work of their counterparts in Doctor Sivanas brood once their powers were restored. Like many Golden Age Shazam stories, though, it managed to take things in unexpected directions. Instead of visiting cavemen or ancient Rome, the Sivanas were plundering ancient and futuristic versions of Atlantis.
1 Green Lantern Carried The JSA After Per Degaton
All-Star Comics #35, June 1947
As chronicled by John Broome, Irwin Hasen, Paul Reinhart, Lee Elias, and the legendary Joe Kubert, All-Star Comics #35 was the first time-travel adventure for the Atom, Dr. Mid-Nite, Johnny Thunder, and Hawkman. Other members of the JSA, Green Lantern, Wonder Woman, and the Flash had already traveled in time.
When the JSA learned the time-altering villain Per Degaton had changed history, they pursued him into the past, using the power of Green Lantern's ring. The heroes fought to prevent a pivotal loss by Alexander the Great. When they stopped Per Degaton's plan, the timeline reasserted itself, erasing the world's collective memories of Per Decaton's alternate timeline as history repaired itself.