Mercy Graves was a tough young woman with a checkered past, who served as Lex Luthor's personal bodyguard and chauffeur. Mercy was loyal and respectful to Luthor, but never servile. There are some hints that she was attracted to Luthor, and fiercely resented any woman who came between them. When Luthor became unusually taken with Lana Lang, Mercy secretly followed her and discovered her passing information on Lex's activities to Superman. Mercy was proud of what she'd done, though Luthor took out his disappointment on her.
When Luthor was abducted by Brainiac, she once teamed up with Superman to find him. Superman was baffled by her loyalty to Luthor, initially believing that she had some dirty secret that Lex was threatening her with, and taken aback to hear her say she served Luthor willingly. Superman tried to convince her that Luthor did not return her loyalty, but she refused to listen.
In the ensuing battle with Brainiac, Mercy was pinned under a pile of fallen machinery while the room was caving in. She called for Luthor to help her, but he chose to save himself, leaving her to die. Instead, she was saved by Superman. Afterwards, she continued to serve Luthor, probably trying to forget his betrayal.
When Luthor and the Joker worked together in the three-part "World's Finest", Mercy had an intense rivalry with Harley Quinn, to the point of getting into a physical fight with her. Harley later gagged Mercy with duct-tape and tied her to a robot that was fighting Batman and Superman. She was rescued by the two heroes upon the robot's defeat but recieved severe injuries in the proccess. Ultimately it was Mercy who had the last laugh when Harley was publicly arrested, raving insanely the whole time, and Mercy was seen watching it on the televisions, hurting herself from laughing so hard.
When Luthor went to prison, he appointed Mercy as acting head of LexCorp. Somewhat to her own surprise, she thrived: not only did she save the company from the slump caused by Luthor's arrest, she made it more powerful and profitable than it had ever been. When Luthor, a fugitive from the Justic League, appeared in her (formerly his) office pleading for help, she coldly rejected him. According to her, she had "figured out" that the only reason he left LexCorp in her care was because he thought of her as the only one so slavishly loyal to him that she'd hand it back when asked. Given this unflattering assessment of her character, and her undeniably excellent performance as a CEO, she said she no longer had to lick his boots. Luthor responded with violence, and she reluctantly guided him to Professor Ivo's residence, as he was seeking a cure for his Kryptonite poisoning.
Although the Justice League was searching for Luthor, she concealed his whereabouts and continued to aid him, though reluctantly. Even as she did so, he taunted her, saying she couldn't resist the attractions of his power and intelligence (implying that at some point in the past their relationship was more than platonic). But after he was humiliated by the android AMAZO and sent back to prison, he called her on the phone, demanding that she obtain lawyers and medical experts for him. She coldly hung up on him.
Still later, however, after he was released from prison, Luthor regained control of LexCorp, and Mercy returned to his right side, implying her new found self-confidence had gone.
Mercy later appeared in the show The Batman along with Luthor. In this show she is depicted as black haired and of Eurasian descent.
She also appears in the show Young Justice however in this she has a bionic arm that can shoot a laser. In addition to this she is also given a new uniform. She mainly acts as Luthor"s protection or body guard rather then butler. She has no dialogue in any of her appearances.