Though it's been close to a decade since Smallville ended, the show's version of the Justice League remains one of the biggest live-action superhero teams ever adapted to the small screen. Also, even though there have been multiple DC TV shows produced in recent years, no series since Smallville has even used the Justice League.
The Superman prequel series, which originally aired on The WB (before becoming The CW), lasted for ten seasons as it told the story of a young Clark Kent (Tom Welling) and his journey to become the Man of Steel. Over the course of the first three seasons, Smallville rarely ventured outside Clark's hometown, and mostly dealt with original characters. Starting with season 4, the series slowly began to step outside its comfort zone and wade deeper into the world of DC Comics by introducing various characters from Superman lore, including Lois Lane (Erica Durance).
Smallville didn't just utilize Superman characters. While playing in DC Comics' sandbox of characters, Smallville found ways to adapt some of DC's biggest heroes and villains. Each character would usually be introduced by serving as a guest star or the focus of an individual episode. Gradually, Smallville acquired enough supeheroes to debut their own version of the Justice League in season 6. The team continued to grow as the series went on. Here's every superhero in Smallville's Justice League.
Bart Allen (Kyle Gallner), the fourth comic book incarnation of The Flash, was the first DC Comics hero outside the world of Superman to join Smallville. The speedster was introduced in season 4, before returning in season 6 as a founding member of the Justice League. Bart was recruited by Oliver Queen (Justin Hartley) and, under the name "Impulse", was sent to infiltrate a LutherCorp facility as his first mission.
Introduced in Smallville season 5, underwater superhero Aquaman (Alan Ritchson) had a short-lived romance with Lois Lane before coming back in season 6 alongside Impulse, Green Arrow, and Cyborg as a member of the Justice League. In a season 10 episode, Aquaman revealed that he had accepted his destiny as the King of the Seven Seas and had married his comic book love interest, Mera.
Aquaman wasn't the only DC Comics hero introduced in season 5. During the same season, Clark met Victor Stone (Lee Thompson Young), a former football star who had been turned into a cyborg by his father. Clark helped Cyborg escape from his father and inspired him to be a hero. As "Cyborg", Victor came back into the fold in season 6 when Oliver formed the Justice League.
Of all the heroes who joined Clark on his adventures, none of them have been more important to Clark's story than Justin Hartley's Oliver Queen, who had a recurring role in season 6 as a former friend of Lex Luthor (Michael Rosenbaum), and a billionaire moonlighting as the vigilante Green Arrow. Green Arrow, the leader of the Justice League, played a major role in Clark's journey in becoming Superman. Hartley's character also became a series regular in season 8, and remained on the show until the very end.
Clark Kent doesn't become Superman until the series finale, but that doesn't stop him from being a superhero. Since Clark was still based in Smallville when the Justice League was formed in season 6, he was reluctant to join but still served as a part-time member. However, it didn't take long for Clark's ties to the team to grow stronger. After becoming a full-time member, Clark took Oliver's place as leader in season 9 and later led the Justice League into battle with Major Zod (Callum Blue) and the Kandorian army.
Alaina Huffman's Black Canary was a mercenary hired by Lex Luthor to capture Green Arrow in season 7. After discovering Oliver Queen's true identity, Black Canary nearly succeeded in her plan, but was thwarted by Clark. As it turned out, Black Canary was fooled into believing that Green Arrow was a terrorist. She ended up joining forces with Clark and Oliver and agreed to join the Justice League. Black Canary returned at certain points in season 8, 9, and 10 to help out the team.
Martian Manhunter aka John Jones (Phil Morris) is another of Clark's closest allies in Smallville. In the guise of a police detective, John spent several years watching over Clark in secret, in order to honor a request from Clark's biological father, Jor-El. Martian Manhunter's job was to make sure Clark fulfilled his destiny. In season 6, Martian Manhunter had no choice but to reveal himself to Clark. In the time that followed, John Jones provided guidance for Clark and even joined the Justice League off-screen in season 8.
Serinda Swan's Zatanna Zatarra in Smallville is so far the only live-action version of the DC Comics magician. In her first appearance in season 8, Zatanna tried to use her magic to resurrect her dead father but realized the error of her ways. It was eventually revealed that Zatanna had at some point become a Justice League member. The character only appeared in person one more time in the series, but was referenced on numerous occasions.
Hawkman (Michael Shanks), the reincarnation of an Egyptian warrior, was originally a member of a much older team of superheroes called the Justice Society. He came out of retirement in the Smallville movie event, "Absolute Justice", to battle Icicle, a villain who was tracking down and killing former Justice Society members. In season 10, Hawkman tragically died saving the life of Lois Lane. His funeral was attended by nearly every member of the Justice League.
Courtney Whitmore (Britt Irvin) is the protégé of the Star Spangled Kid, a former member of the Justice Society and a victim of Icicle. Courtney took up his Cosmic Control Staff and became "Stargirl". Her original intention was to reform the Justice Society, but the character instead became more involved with fighting alongside the Justice League.
"Watchtower" is the codename of Chloe Sullivan (Allison Mack), Clark's closest friend and confidante, and the only person on the show to serve as a main character throughout all ten seasons of Smallville. Ever since their high school days, Chloe's resources and tech skills have been some of Clark's greatest assets when it comes to helping people, which is why it made perfect sense for Chloe Sullivan to work as the eyes and ears of the Justice League. She even let the team use her Metropolis apartment as a base.