Lionel Luthor (Earth-2) Season 10

When Clark Kent of Earth-1 accidentally switched places with Clark Luthor of Earth-2 using the Mirror box, Clark finds himself greeted by Lionel in his bedroom with two girls in the Luthor Mansion. After Lionel lectured Clark, they had dueled with blue kryptonite-laced swords.

When Lionel caught his daughter Lutessa sneaking around into Lionel's office to get a hold of a journal that had information regarding the Mirror Box. Before being arrested by his guards, Lionel claimed that she was not a worthy heir to the Luthor name. Lutessa gets a parting shot at Lionel and slaps him before being dragged away.

When Clark goes to the Fortress of Solitude in the hopes of getting help from Jor-El, Lionel is there has the Fortress integrated with Earth technology. Lionel states that he caught Lutessa trying to located the mirror box, which was odd as he had done all he could to destroy any Kryptonian artifacts. Clark lies and claims he asked Lutessa to help in order to destroy the box, and Lionel then claims that Oliver Queen has the box.

This is revealed to be a lie, and Lionel himself had the Mirror Box. He had instead wanted to locate Oliver and to discover if Clark was going to betray him as he once assumed. Lionel stops Oliver from killing Clark using Kryptonite rays and a gun, but then instead of helping Clark, Lionel says that he has failed him as a father, and that if he was a true Luthor he would have killed Lionel by now and Lionel blames himself. Lionel starts to beat Clark with his belt as he rants about how only the strong survive, and how he will be the strongest in this earth, or any other. At this point, Oliver realizes that Clark is the "good one" and turns off the kryptonite. When Clark grabs the mirror box and activates it, Lionel runs towards him in the background.

Unknown to Clark, Lionel made it into Earth-1. While purchasing a newspaper about the Blur, a vendor asks Lionel if he's seen him before. Lionel states that he's merely visiting from out of town unexpectedly. Guessing that he made it back in the nick of time, Lionel says he wouldn't want to miss "how it all turns out", before walking into a crowd.

Lionel researched everything to find out more about his Earth-1 doppelganger. Although he found out that his son Lex Luthor had died, he discovered Lex was "alive" in another way: in the form of Alexander Luthor. When Tess Mercer was walking to her office, Lionel was sitting there waiting for her. He reached out to her, to be the father that she needed and be there for Alexander.

He intended on finding Alexander before Tess did and do right by him. Lionel managed to find Alexander in Suicide Slums, staying in an old apartment. He realized that it was him who attacked Senator Martha Kent in order to kill Clark. Lionel managed to take "back" LuthorCorp and returned Alexander to LuthorCorp; Oliver Queen and later Martha confronted him about his actions. When Alexander found out that Lionel still favored Clark over him in the other world, he decided to do away with both his "father" and Martha. After Lionel was saved by Clark, Lionel watched the Luthor Mansion burned to the ground.

For weeks, Lionel remained in control of LuthorCorp. Lionel went to Cadmus Labs, finding Tess there as well. He vowed that he would have his "son" Alexander, but Tess showed him Alexander’s "remains". In the end, Lionel discovered she was lying by using the remains of another Lex clone and went to find his "son". Lionel realized Alexander was now called Conner Kent, had changed his hair and developed Kryptonian abilities like Clark, and actually had Clark's DNA as well as Lex's. He reached out to Conner, to remind him of his past as he gave him a red kryptonite ring. Lionel then took Conner to a captured Lois Lane who was going through his files in his office about being the "fake" Lionel Luthor. Before he could put an end to Lois by shooting her, Conner whisked her away. He realized that the red kryptonite made Conner more excited in his infatuation with Lois, and then continued to track Conner to back to the Luthor Mansion where he had to subdue Clark Kent with Kryptonite. He went there to try to remind Conner about the fact he is still a Luthor, but Conner remained to be on Clark's side.

Returning to his empire, Lionel was eventually thrown out by Tess who regained control of the company and started tracking him of every step he makes. Late at night, Lionel paid his respects at Lex's gravesite. As he was leaving, Lionel was approached by Darkseid.

At some point Lionel discovered that Lex had instituted another project deep inside the chambers beneath the Luthor Mansion to keep himself alive after the events at the Fortress of Solitude. Through Lex's plan the best pieces of his imperfect clones would be grafted into a new body that would be a masterwork to bring Lex back to life. While almost everything had been recreated, Lex did not have a heart.

Lionel launched a plan to capture Tess so that her heart could be removed to save Lex's life. Shortly before the surgery, Tess escaped and shot Lionel in the chest, killing him.