The recent release of Justice Society: World War II shines a welcome light on the Justice League's predecessors. The JSA made its debut in All Star Comics #3 as the first superhero team in comic book history. They appeared from 1940 to 1951, and some characters were revamped as members of the Justice League of America during the Silver Age. Later continuity established that the Justice Society existed on Earth-2.
After Crisis On Infinite Earths, the JSA and the JLA merged and now both exist on New Earth, with the JSA in the past and the JLA in the present. This convergence created multiple versions of some characters. Then Flashpoint reset the DC Universe again. Hopefully the success of this movie means fans will get more JSA content in the future — and maybe meet members who haven't been in the spotlight lately.
10 Magog (David Reid)
Magog originated from the Kingdom Come miniseries, later established as taking place on Earth-22. He reappeared post-Crisis as Lance Corporal David Reid. After touching a fragment of the Old God Gog, he developed the power to project energy and joined the JSA. Not long after the team met the mysterious healer Gog, a missile hit Reid and killed him. Gog revived him.
Now known as Magog, Reid preached Gog's will and refused to believe that Gog was an enemy until he saw his needless cruelty. After the JSA took down Gog, Magog had his own short-lived series. Since Flashpoint, Magog tried to kill Superman, had his staff confiscated by Wonder Woman, and turned into a ten-year-old who is presumably very grounded.
9 Miss America
Joan Dale had a dream that the Statue of Liberty came to life and gave her superpowers. It turned out that they came from a secret government experiment, but she's still remarkably patriotic. In 1942, she joined the JSA…as their secretary
Due to a post-Crisis retcon, lots of Wonder Woman's adventures with the JSA were attributed to Miss America. Another retcon introduced Hippolyta, another Wonder Woman, as a member of the Justice Society. It's unclear as to which of them now gets the credit.
8 Liberty Belle (Libby Lawrence)
Elizabeth "Libby" Lawrence was another patriotic WWII era hero, an Olympic athlete who escaped the Nazis three times. During the last escape, she jumped overboard a sinking ship and swam across the English channel to safety. She discovered that she had a connection to the Liberty Bell and became more powerful when it rang. Libby would later develop sonic powers.
In 1941, she joined the All-Star Squadron, an emergency wartime conglomeration of the JSA and other American superheroes. Libby eventually settled down with teammate Johnny Chambers. She came out of retirement during Infinite Crisis, but ended up losing her powers.
7 Sandman (Wesley Dodds)
There are many DC characters named Sandman, but Wesley Dodds was the first. His trademark gas mask protected him from the sleeping gas he used on his enemies. His main power was his cryptic, prophetic dreams. One of the original JLA members, he was created in 1939 but lost popularity in the 1940s.
His comic was revived in the '90s, but still set in the '30s. Dodds was one of the few superheroes to live to old age (multiple times, but that's another story). Eventually, he ended up jumping off a cliff to his death in order to protect the secret identity of Dr. Fate. Since then he's been reanimated as a Black Lantern (twice!), but the true Wesley Dodds is long since dead.
6 Amazing-Man (Markus Clay)
When the JSA was trying to find new members, Power Girl and Earth-22 Superman attempted to recruit Markus, the grandson of the original Amazing-Man. He agreed, was a part of the aforementioned Gog fiasco. Markus was deeply religious, and the first one to connect with Gog.
He was pro-Gog until the god's "rooting into the Earth" scheme was revealed — that really turned off a lot of people. He then assisted the rest of the JSA in taking Gog down. Markus became part of the newly reformed All-Star Squadron during Final Crisis. Afterwards, he left the JSA to create his own team focused on Hurricane Katrina relief.
5 Anna Fortune
Anna Fortune appeared in JSA All-Stars #5 in time to save the team by capturing the King of Tears. She revealed she had been sent by Dr. Fate, and attempted to teleport the group to the Subtle Realms to rescue a teammate. However,, she messed up the spell and immediately released the King of Tears again. After defeating him, the All-Stars recruited Anna despite her abysmal trial run.
She never revealed her connection to Dr. Fate, but seemed to enjoy making vague references to time travel. Unfortunately, she didn't have time to reveal her presumably epic backstory before Barry Allen reset the DC Universe during Flashpoint.
4 Starman (Jack Knight)
Golden Age hero Ted Knight was well-known as Starman, and he eventually got married and had two sons. David Knight looked up to his father and was eager to take on the mantle of Starman. Jack, on the other hand, couldn't stand superheroes. David tried to be Starman and was, of course, immediately murdered by an old Starman nemesis. Jack decided to try his hand at heroics, in order to protect his father and avenge his brother.
The murderer, Mist, died, and his daughter took on his role. She managed to get under Jack's skin to the point that he became a better person out of pure spite. He ended up joining the JSA and had a long, successful career before retiring to San Francisco.
3 Earth-22 Superman
Earth-22 Superman could really use a hug. On Earth-22, the Joker killed every member of the Daily Planet's Staff (minus Clark) and Magog killed him in response. After Magog was pardoned for the murder, Superman lost faith in justice and retired. Magog led the Justice Battalion, a vigilante team that used excessive force with no regard to civilian casualties.
Wonder Woman convinced Superman to create the Justice League, with Lex Luthor and Batman heading up their own factions. A battle between them all ended in a metahuman bomb exploding, and Superman fell through a portal to New Earth. He joined their Justice Society for awhile before finding out the explosion wasn't necessarily a world-ending event as he had assumed. Clark returned to his own world to salvage what he could.
2 Damage (Grant Emerson)
Grant Emerson had explosive, hard-to-control powers. He tried to be a superhero, but caused enough collateral damage (hence the name) to hurt people and get him into legal trouble. He was court ordered to join the New Titans, and was a valuable member of the team. After a while, Grant left to find his parents, violating his parole.
Arsenal later managed to have his charges cleared so he could rejoin. He then went on to join the government sponsored Freedom Fighters. Damage was one of the few survivors of a battle with the Secret Society of Supervillains, but his face was severely scarred. He joined the Justice Society, but was killed by a black lantern.
1 Earth-2 Johnny Thunder
As a baby, mystics from Badhnesia kidnapped Johnny Thunder, as they needed him for a ritual. He was given a genie named Yz as part of a world domination scheme, which never came to fruition. He ended up back in the U.S. without any knowledge of what had happened to him. Johnny could summon Yz with the words Cei-U, but didn't know it. Thus, he accidentally summoned it whenever he used the phrase "say, you".
Johnny was a comedic, bumbling character, who managed to join the Justice Society by accident. Post Crisis, he joined other JSA members in a constant battle in Limbo. Upon returning, he struggled to adjust to his new life. He eventually lost Yz, who was found by Jakeem Williams. After Johnny died in battle, Jakeem wished for Yz to save him, which it did by combining the two of them into an entirely new entity.