|“||I have this feeling that you'll never fulfill your great destiny until you meet your greatest challenge.||„|
|~ Tess to Clark Kent on his destiny.|
Tess Mercer (born Lutessa Lena Luthor) is Lex Luthor's former protégée and younger, half-sister and Lionel Luthor's illegitimate daughter.
Shortly after Lex's disappearance during a private expedition to the Arctic, Tess was given control over all his projects and his finances, inheriting the role of acting CEO of LuthorCorp and publisher of the Daily Planet. In her quest to find out what had happened to Lex, she began to realize that there was something very unusual about Clark Kent. Tess Mercer had her own metahuman agenda and an unusual approach to saving the world.
With the help of remaining records left by both Luthors, Tess managed to discover Clark's secret in less than a year. Unlike Lex, however, she began to see Clark as a hero and savior rather than a threat to humanity. She diverted some of the devotion that she'd had for Lex onto Clark, despite using unconventional methods to prove it.
For a long time, Tess was dedicated to maintaining the Luthors' legacy and was completely loyal to Lex, whom she considered a personal mentor. However, after Lana Lang revealed to her that Lex had implanted an optic camera into her brain to survey her movements in Smallville, she understood that his faith in her had been a lie. She realized that she had left behind a life in Star City as a marine biologist for a man that never trusted her.
Tess felt Lex’s betrayal deeply and sought a personal revenge. She announced his ‘death’ in a front page issue of the Daily Planet and proceeded to cut off his access from all Luthor bank accounts, thereby leaving Lex without any resources to continue his life support. Finally, she asked her former love and Lex's lifelong arch rival, Oliver Queen, to help her merge LuthorCorp with Queen Industries. Tess assumed absolute control over all Luthorcorp businesses and assets, successfully removing Lex’s access to the dynasty.
After learning about Clark's secret and being guided by voices coming out of the Orb, Tess released the power contained within the Kryptonian device, which allowed Major Zod and his army to be reborn on Earth. Tess thought that the Kandorians would be like Clark Kent, and in this way she thought she was be saving the world. Tess helped Zod to achieve some of his goals, but all with the intention to protect and empower her own plans. However, her plans were affected when she was summoned by an old organization to which she briefly belonged, and was forced to go underground to prevent an assassination attempt on her life.
After being rejected by Oliver, whom she trusted the most, by Zod and everyone else she knew, Tess realized that she had lost everything in her quest for power. In an attempt for redemption, she faced Zod and tried to stop him from destroying the Earth, but he used his heat vision to burn her, rendering her unconscious and bleeding. Tess helped Clark use the Book of Rao from her hospital bed and apologized for everything she had done.
Unable to bear the severity of her burns, Tess died in the hospital of cardiac arrest. She was mysteriously resurrected, waking in Cadmus Labs, where she found hundreds of Lex clones. Tess started to take care of what appeared to be a young clone of Lex whom she believed was an innocent little boy. Clark Kent rescued her from the lab and their relationship finally began to shift into a friendship. Things started to become more complicated than she expected due to the latent presence of Lex's mind inside the little boy, but was able to convince the genetically engineered version of Lex to have a change of heart with Clark's help.
With a second chance to redeem herself, Tess decided to start doing things right and chose to help Clark and Oliver in their fight against crime. Soon, she was able to obtain a place in their team of heroes and given the command of Watchtower. However, her loyalty was ultimately tested after learning that she was Lionel's daughter, consequently making her a Luthor; and her situation was aggravated when she discovered that she had been resurrected to serve Darkseid and dueled against a Lionel Luthor of a parallel world.
After a long struggle against her dark side, Tess finally chose a side in the battlefield and finally was killed by her brother Lex, but not without getting the redemption she longed for by erasing all of Lex's memories and thereby protecting Clark's secret. Thanks to an unexpected property of the Neurotoxine however, her conscience survives inside of Lex's mind and so is later rescued by the team and resurrected in a cybernetic form.
As an artificial intelligence, called Tess 2.0, she succeeds to overcome her obsession for revenge on her brother and rejoins the Justice League, becoming Watchtower once again while Chloe is on maternity leave.
- Tess' character is partially based on Mercy Graves, Lex Luthor's personal assistant and bodyguard.