Smallville introduced many new townspeople and villains over the course of the series, offering Clark Kent (Tom Welling) consistent challenges in the form of enemies and allies.
Many of these guest appearances include Hollywood stars from renowned franchises, such as film icons who collaborated with Star Wars and High School Musical, reflecting the show’s impressive casting and presence in the world of television.
Amy Adams, Paul Wesley, and 5 other actors who appeared on Smallville
7) Carrie Fisher

Chloe Sullivan visits the Daily Planet after high school graduation and university registration. She is received there by Editor-in-Chief Pauline Kahn, played by Carrie Fisher, who is best known for playing Leia in Star Wars movies. Pauline finds that Chloe won the high school Daily Planet column due to Lionel Luthor's intervention, rather than on merit.
Chloe, in desperation to be credited, sets out to investigate a sorority house linked with vampire attacks and submits an article on the story. Pauline, after reviewing Chloe’s reporting, finds Chloe to be worth another chance and hires Chloe in an entry-level role, with the advice that the future at the Daily Planet comes with a lot of dedication and hard work.
6) Amy Adams

Before Amy Adams played Lois Lane in Man of Steel, she appeared in season 1 of Smallville as Jodi Melville, a character affected by meteor rocks. Jodi's exposure to vegetables grown in kryptonite-laced soil leads her to lose significant weight and develop an abnormal hunger. She requires fat to maintain her metabolism, which allows her to absorb fat from animals and humans.
The changes in Jodi's body influence her relationships and interactions at Smallville High, particularly with Pete Ross (Sam Jones III). During an episode, Jodi nearly harms Pete while trying to manage her new appetite. Clark Kent intervenes to prevent harm and ensures Jodi receives medical attention. Jodi’s storyline reflects the impact of kryptonite on ordinary residents and emphasizes themes of self-image and personal challenges.
5) Cobie Smulders

In season 4, Lex Luthor’s reputation as a womanizer is addressed when a former romantic interest, Shannon Bell (played by Cobie Smulders), targets him for revenge. Shannon and Lex previously had an affair that ended when Lex broke off their relationship and gave her diamond earrings.
Shannon later lures Lex to a hotel room where he discovers another former lover’s body beside him, triggering a police investigation. Lex is unable to recall what happened, and the situation escalates as Shannon reveals her identity and motivations.
She attempts to harm Lex by starting a fire at his residence, but Clark Kent intervenes to stop her and prevent further harm. This storyline portrays the consequences of Lex’s earlier personal choices and the role played by guest characters in episodic conflict.
4) Tori Spelling

Tori Spelling guest stars as Linda Lake in season 6 of Smallville. Linda is the gossip columnist at the Daily Planet whose shape-shifting ability permits her to remain hidden and listen in on private conversations. She discovers significant facts, including the wavering of Lana Lang over Lex’s proposal and the extraterrestrial origins of Clark Kent.
Linda prints out information on the relationship between Lana and tries to write about Clark’s identity. Chloe Sullivan interrupts by disabling Linda’s computer to prevent the article. After Chloe gets into a fight with Linda, the argument is concluded when Linda is hit by Lana's car, and her body transforms into water.
3) Paul Wesley

Paul Wesley in Smallville portrayed Lucas Luthor in season 2, who was the younger half-brother of Lex Luthor. Lex discovers Lucas in the episode titled "Prodigal" and relocates him to Smallville in an attempt to acquire family business control. The loyalties of Lucas shift when he is offered money by their dad, Lionel Luthor, to get Lex out of the business.
Lucas then attempts to gain sole possession of the family interests, including the Talon. He also finds out that his dad's blindness was faked and that he participates in Lex's fake kidnapping to dupe their dad. The episode portrays the strained relations as well as family power struggles.
2) Lucas Grabeel

Lucas Grabeel appeared as a guest in Smallville twice as different characters. During season 6, he portrayed teen Lex Luthor in an episode that was based on Lex's time at boarding school. The story describes young Lex in conflict with his friend Duncan after the latter bullies him at school.
Again, in season 10, Grabeel returned as Alexander Luthor and Conner Kent, the latter of whom is the hybrid clone of Lex Luthor and Clark Kent. Conner Kent possesses multiple supernatural abilities like Clark and is the leader of the teenage superhero squad known as Superboy.
1) Adam Brody

Adam Brody was the actor who played Justin Gaines in season 1. Justin is an accomplished art student gifted with telekinetic powers after being in a car crash that injured his hands. Justin uses his powers to pick up objects with his mind and seeks revenge against those who he feels were responsible for affecting his future as a cartoonist due to the accident.
During his time in the series, Justin has a crush on Chloe Sullivan, although the latter is unaware of the same at the beginning. Chloe discovers Justin's powers after seeing elaborate illustrations of gruesome happenings in his artwork, which then causes the latter to persuade Clark Kent to investigate the same.
Clark acts in time to prevent further devastation, including that of Chloe. The episode reflects on the consequences of immediate powers as well as the misery witnessed in the wake of the meteor shower.
All episodes of Smallville are currently streaming on Hulu.