He features from the pilot episode until the season seven finale, and has been played continuously by Michael Rosenbaum, with various actors portraying the character as a child or teen throughout the series.

Lex is an inquisitive person, and it is that curiosity that drives him to attain as much power as possible as the series progresses—it will ultimately lead him to being Clark's greatest enemy.

Years later as a young adult, Lex first meets Clark Kent (Tom Welling) saving his life from drowning and the two quickly become friends.

He hires Roger Nixon (Tom O'Brien), a reporter for the tabloid newspaper The Inquisitor, to discover how he survived the automobile accident where Clark saved him from drowning.

[19] His curiosity into the symbols, which he believes to be alien in nature, results in Brainiac (James Marsters) arranging him to be possessed by the spirit of the Kryptonian criminal Zod.

[25] The device, an orb he finds in the mantle above a fireplace in the Luthor mansion,[26] leads Lex to the Fortress of Solitude, where he is confronted by Clark.

[31] Season ten revealed that at some point prior, Lex manufactured a number of clones, but the majority of them are flawed and age at an accelerated rate.

One clone of Lex (Mackenzie Gray), aged approximately twenty years older than the original, attempted to get revenge on Clark by trying to kill Lois Lane (Erica Durance) but died before he could finish.

There have been four other actors that have performed the role; Matthew Munn, Wayne Dalgish, Lucas Grabeel, and Connor Stanhope have all portrayed Lex Luthor as a child in various episodes throughout the series.

Specifically, he delighted in the chance to "go overboard", like he did in "Hug" where his character pulls out a machine gun and shoots everything in sight; to the actor, this gave the audience a glimpse into who Lex was becoming.

[35] After seven seasons of portraying Lex Luthor on Smallville, Michael Rosenbaum decided to move on with his acting career, so he departed from the show.

[39] Rosenbaum believed that Lex was trying to be a hero in season one, but that his character showed signs of having to fight "ambiguity" and stay on the straight path.

[37]Season two delved deeper into Lex's darker moments, from the time he wavers to save his father's life, to his outburst at Jonathan for what he feels is unfair treatment.

[40] Season three's "Memoria" finally explained the mysterious circumstances surrounding the death of Lex's infant brother, Julian.

By the time "Aqua" came around, Lex had removed the gloves, as there is no friendship with Clark that he needed to worry about, and his dark side began to show its face.

In this alternate reality, without all the power and money that he had originally had, Lex is unable to save Lana, who dies after giving birth to their second child.

[44] In the season two premiere "Vortex", Rosenbaum requested Greg Beeman to film a close-up of him after he shoots Nixon, in an effort to open a window into Lex's darker side.

As writer Steven S. DeKnight describes it, the audience gets to see a moment where Lex shows how he still feels like an outsider, and that he views Clark as this "perfect person".

In Smallville, Lex is usually given a "glass, steel [colored] background", and he is dressed in a lot of black, grey, and "cool tones" clothing like purples and blues.

[42] Reviewer Brian Byun expressed that the choice to explore the friendship between Clark and Lex, before they become sworn enemies, which was something that had been used in the past but never to the depth of what Smallville is doing, helped keep the show from becoming "Dawson's Creek with superpowers".

Rosenbaum and Annette O'Toole (Martha Kent) agree that the only person that could give Lex that love is his mother, who died when he was a child.

This need to fill that emptiness was fulfilled in "Void", when Lana took a drug to induce death so that she could see her parents in the afterlife.

[44] Michael Rosenbaum was nominated multiple times for the Saturn Award category of Best Supporting Actor in a Television Series for his performance as Lex Luthor.

[61] In Smallville: Dragon, Lex throws a party at his mansion for the local teenagers, that is ultimately crashed by a reptilian creature that was created by the meteor rocks.

This leads to a proposal with General Sam Lane to create a joint venture between LexCorp and the Pentagon for the company's project, "Guardian Defense Platforms", which involves monitoring the world's metahuman and extraterrestrial communities.

In addition, Otis discovers that the toxin not only erased Lex's memories and enhanced his intelligence, but also caused him to mentally bond with Tess's consciousness when she poisoned him.

[67] Michael Rosenbaum was approached by Warner Bros. and the Arrowverse television series' producers to reprise his role as Lex in the crossover "Crisis on Infinite Earths", but he declined, instead gaining a small mention as the President.

[68] His character, however, makes a cameo in the background of the comic book tie-in Crisis on Infinite Earths Giant along with other iterations of Lex Luthor including those from the other Superman-related media and adaptations such as the iteration based on the portrayal by Gene Hackman (with this Luthor remarking that the Earth-38 iteration reminds him of his nephew Lenny, a character from the film Superman IV: The Quest for Peace portrayed by Jon Cryer), due to it is centering on Cryer's Lex and Tyler Hoechlin's Superman from the television series Supergirl.

It is revealed that Lex has formed "The Council of Luthors" with his parallel universe counterparts after contacting them during Smallville: Season Eleven, with him being identified as 167 after his Earth's designation, for schemes to eliminate Supermen from the multiverse so that they may conquer it without their enemies' interferences, and established an orbiting satellite base above Earth-99 (where its Superman was killed by Batman).

The formation of the council has also led to the Supermen to form their own alliance to counter them, though it is not revealed of whether Clark had joined them prior to him giving up his powers for his family.