Time travel takes on a lot of forms, and comicbook/superhero writers have certainly done their fair share in broadening the tradition. This article covers some of the earliest instances of time travel concerning comics and superheroes.
The Shadow (radio series)
Chronologically, this old-time radio episode of The Shadow is the first instance of time travel encountered by an actual superhero. “The Man Who Murdered Time”, originally broadcast on January 1, 1939, is about a dying man and his attempt to use a time machine not for travel but rather to replay one day for eternity. No one should have been able to do anything except exactly what they did that day, but the Shadow (or ‘Lamont Cranston’…I guess he flunked out of Alter Ego Naming 101) was trained in Asia, and apparently the training produced a type of ‘ iron will’ that made it difficult for the time machine to control him, as well as others who are under the Shadow’s direct influence. And apparently none of his trainers survived, or else he could have mustered an army of time-busting Hindus to make short work of the plot.
FUN QUOTE: “Instantaneously time will take up where it left off, but you put the machine into operation, and so will come what you thought to destroy forever – the new year, the bless’ed new year. That means new hope for the good and the innocent people of the world, while for you it will bring what God decreed for you…Death!” – The Shadow
You can listen to the episode (and a few dozen more, for free) at Old World Radio.
Mark Swift and his Time Retarder (comic book, Slam Bang comics #1)
Mark Swift, the young orphaned friend and sidekick of a school teacher-turned-timelord named Rooney Kent, was the first comic book character (Slam Bang comics #1 is cover dated March 1940) with a time travel device, which Rooney used to teach Mark about history…by subtly altering it, I guess. Kent and Swift built the device themselves, Kent having “…discovered the amazing principle of time-travel”, without any further elaboration about just HOW he discovered it, or even what the amazing principle actually was. Oh, but trust them…it was AMAZING! The introductory paragraph mentions that Mark is “…liked by everybody.”, which means you have to like him, unless you don’t consider yourself part of everybody, you cynical misanthrope. All this from the mind of Otto Binder, who went on to create (or co-create) Mary Marvel, Black Adam, the Legion of Superheroes, Braniac, Supergirl, and gold from base metals.
You can read all of their adventures online at Digital Comics Museum.
Brick Bradford (comic strip)
For a comic strip that lasted over 50 years straight (not to mention the 1947 movie serial…although I did just mention it, so…um…AWKWARD), you would think that Brick would have made more of an impact on culture than he did…which seems to be none at all. From 1933 to 1987 Brick adventured on Earth, in space, and (starting on October 17, 1937) through time. Brick and company typically went forward to the future, while poor Mark Swift had to settle for going back in time. Brick’s ship was called the Time Top, and was apparently not bound by time. I think his first attempt at this type of device was his Time Yo-Yo, which would almost reach its destination, then be drawn back to its starting point. Then moving toward the destination again; then back. Lather. Rinse. Repeat.
Anyone interested in reading more about him can find literally thousands of his comics strips at I Love Comix.