Alexander Joseph "Lex" Luthor, Jr. is a fictional character in the DC Extended Universe based on the DC Comics supervillain of the same name. He is portrayed by Jesse Eisenberg. Luthor first appeared in the 2016 film Batman v Superman: Dawn of Justice, pitting Batman and Superman against each other in an attempt to eradicate the two superheroes. He also appears briefly in Justice League and its director's cut. Eisenberg's portrayal of Lex Luthor has been described as unorthodox compared to most depictions of the character, with his performance in Batman v Superman receiving mixed reviews.

On January 31, 2014, it was reported that actor Jesse Eisenberg was cast as Lex Luthor, one of Superman's greatest foes, in the DCEU film Batman v Superman: Dawn of Justice. Screenwriter David S. Goyer talked about the character in the Man of Steel sequel as a Bill Gates-like billionaire. Director Zack Snyder talked about seeing a modern take as a combination of Richard Branson and Brad Pitt. Eisenberg had also played real life billionaire/entrepreneur Mark Zuckerberg in the film The Social Network, which Kase Wickman of MTV noted and used to draw comparisons between Luthor and Zuckerberg, especially with the latter being portrayed as ruthless in said film.

Eisenberg revealed in an interview with Chris Van Vliet following the film's release that he had "no idea" which character he was auditioning for at first and expressed doubt when Snyder later revealed it was for Lex Luthor, though he later accepted after reading the script. He stated that the Luthor role "had everything in it that I really like in a character. It was kinda a guy who seems eccentric and possibly nice to the public and yet inside is really harboring these horrible feelings. And I thought, 'I could do this character really well.'" As of 2020, Eisenberg remained open to portraying Luthor again in film.

"Lex Luthor is often considered the most notorious of Superman's rivals, his unsavory reputation preceding him since 1940. What's great about Lex is that he exists beyond the confines of the stereotypical nefarious villain. He's a complicated and sophisticated character whose intellect, wealth and prominence position him as one of the few mortals able to challenge the incredible might of Superman. Having Jesse in the role allows us to explore that interesting dynamic, and also take the character in some new and unexpected directions."

— Zack Snyder

The DCEU iteration of Luthor, as portrayed in Batman v Superman: Dawn of Justice, is noticeably different than in most comic depictions as well as Gene Hackman's portrayal of the character in the 1978–87 Superman film series. Luthor presents himself in public with a welcoming, but frantic tech bro persona, in a similar fashion to Zuckerberg. However, he is in reality a scheming, paranoid figure with sociopathic tendencies who is obsessed with bringing Superman down. He is also characterized as a misotheist, hating God and other god-like beings such as Superman as he perceives the gods failed to protect him from abuse received from his father, Lex Luthor Sr. (mentioned by Luthor as the "Lex behind LexCorp"). Eisenberg made an effort to differentiate his take on the character from that of Hackman and Kevin Spacey, and also states that his character views Superman as a genuine threat to humanity rather than simply someone to destroy. Screen Rant noted that the Luthor portrayed in Batman v Superman bears similarity to another younger iteration of Luthor in the Superman: Birthright comic series, which, like the Lex Luthor of Smallville, was portrayed as "manic and awkward," in addition to being mentally disturbed.

Also unlike most depictions of Lex Luthor, Eisenberg's version is depicted with authentic, shoulder-length hair as opposed to being naturally bald, though he gains his comic-accurate bald look after being clean-shaven in prison at the end of Batman v Superman and retains it in both versions of Justice League. Despite this, there have been several instances in the comics in which Luthor has been portrayed with hair, including Superman #10 in which Superboy accidentally causes Luthor's baldness, and later comics which depict Luthor's illegitimate son, Lex Luthor II, with a full head of hair.

In an analysis of Batman v Superman, film critic Jordan Johnson writes that Eisenberg's Luthor represents meaninglessness and the ego of mankind, which is jeopardized by the existence of the godlike Superman. He writes that "The casting of Jesse Eisenberg, decidedly recalling his portrayal of Facebook mogul Mark Zuckerberg, updates Luthor as perhaps the first truly millennial movie villain: secular, arrogant, entitled, narcissistic, obsessive in his quest to tear down the values of the old guard." Travis Bean of Forbes opined in 2020 that Luthor's characterization in the film was part of a "commentary on our society's seemingly perpetual moral-spiritual-cultural conflict," and that Luthor specifically represented "the younger generation's rampant ego and lack of faith in humanity" when compared to Henry Cavill's Superman and Ben Affleck's Batman. The book Adapting Superman: Essays on the Transmedia Man of Steel includes two chapters that incorporate analyses of Eisenberg's Luthor: the chapter "Through the Lens of Dr. Frankenstein: Luthor as Prometheus," which analyzes Eisenberg's Luthor as a version of the character that "draws attention to Promethean and Frankensteinian themes," and the chapter "Forging Kryptonite: Lex Luthor's Xenophobia as Societal Fracturing, from Batman v Superman to Supergirl," which analyzes Eisenberg's Luthor as part of "a representation exploring the cultural effects of encroaching xenophobia" from society to the family "[i]n the years surrounding the 2016 United States presidential election."