Quark/"Scarlett McKenzie" first appeared in " Havok and Wolverine: Meltdown" #1-4 (1988-1989). Her real name is unknown. She was reportedly a Soviet psychologist and former head of an asylum. She did pioneering work on the effect of assigned roles to human behavior.
Quark entered an alliance with Dr. Neutron and General Meltdown. Meltdown was a Soviet mutant or mutate with the power to absorb radiation. However he would need a jumpstart in the form of a nuclear explosion to really activate his powers. He also figured needing someone to metabolize the power for him to ensure the best absorption rate, powering him to the highest level possible. Havok was chosen for the role. Quark set about to recruit the former X-Man.
She located her target in a Mexican bar along with Wolverine. The two mutants were involved in a bar brawl escalating to a gunfight. Fleeing the bar in haste, the duo encountered "Scarlett" in the parking lot. She was wearing a black wig and dark sunglasses which hid her eyes. The two former X-Men hijacked her car as a getaway vehicle, deciding to take the "innocent bystander" with them.
"Scarlett" calmly re-applied her make-up while her companions were attacked by two agents of Dr. Neutron. Seeing the mutants effortlessly achieve victory, confirmed their identities for her. She pulled a gun from her purse and shot them both. Instead of bullets, the gun contained capsules infecting them with Bubonic plague. Six of them were enough to take care of Wolvie, healing factor or not. She proceeded to abduct Havok, having no use for the unconscious Canadian.
Wolverine recovered a while later, only to be told Havok was dead and buried. Not convinced, Logan dug up the grave. Finding out the body buried inside was not Alex Summers. Meanwhile, the real Alex had been transported to a hospital facility owned by Dr. Neutron. "Scarlett" now appeared with red hair and green eyes, posing as the attending nurse. Her "treatment" involved drugs making Havok susceptible to mind-control.
Havok awakened to discover "Scarlett" informing him of his situation, recovering from the plague. His friend was reportedly buried. She allowed him to watch television, only it was subliminally enhanced. Alex felt strongly attracted to his nurse. But was not too impressed with the television, noting his training by Professor X allowed him to recognize subliminal influences. He fried the device with a plasma bolt. "Scarlett" pretended to be surprised that her patient was superhuman.
She worked for quite a while to earn his trust and ensure that he desired her. She discussed their further plans with Dr. Neutron. He decided a stronger drug dosage was in order. Quark noted that Alex was convinced his friend (Wolvie) was still alive and determined to find him. She decided to use that belief for their own ends. She arranged a meeting between Havok and a supposed CIA agent asking questions about the two mutants. The agent convinced Havok that Wolvie was held prisoner somewhere in Poland.
The agent slapped "Scarlett" to the ground in order to intimidate Havok. As intended, the infuriated Alex knocked the man out and escaped the hospital. Taking the nurse with him. She arranged for a bi-plane to fly them away. Ironically, Wolvie arrived in the hospital moments later. Finding his friend missing again.
"Scarlett" continued helping Havok get to Poland, though Alex had trouble believing how smoothly things were going. She contacted Dr. Neutron to make further plans and ensured Wolvie stayed on their trail. Neutron was slightly disturbed to note that Quark seemed genuinely interested in Havok and might be becoming lost in her role. Essentially becoming the mask she wore.
"Scarlett" convinced Alex that the convenient flights taking them closer to their destination were arranged by one of her former boyfriends, a well-connected drug dealer. He believed her and the two soon became lovers. The two arrived to the Polish facility on horseback, only to find a brainwashed Wolvie attacking them with lethal intentions. Havok had to let his power loose, causing Wolvie to suffer cardiac arrest. Distraught at "killing" his fiend, Havok swore vengeance at those responsible for the event.
Alex and "Scarlett" buried Logan in a shallow grave. While consoling him, "Scarlett" led Alex towards clues that their enemies' next target was a nuclear facility of India. They headed for the Tarapur reactor of Maharashtra, India. By then, the new couple had strong feelings for each other. "Scarlett" was wandering if Havok could kill Meltdown and set them both free of his manipulations.
They found the Tarapur facility already suffering massive radiation leakage. They wore radiation suits before entering, assuring each other of their mutual love. Havok gradually absorbed the radiation. Then, Meltdown introduced himself. Havok kept attacking him, failing to realize that his opponent fed on the energy of said attacks. "Scarlett" realized that Meltdown was about to kill them both. She tried to warn Havok in time. But Meltdown saw what could drive Havok over the edge with rage: killing his lover before his eyes. "Scarlett" was incinerated with a single energy blast.
Meltdown indeed gained the power he craved. But the arriving Wolvie helped weaken the man's body enough that it could not restrain the energy any longer. Meltdown was vaporized as a result. Havok was left mourning his lover, noting how "Scarlett" sacrificed herself in order to warn him. Wolvie realized "Scarlett" was the one who led them into this mess in the first place. But kept silent, not daring to further hurt Havok emotionally.
Quark was a skilled psychologist and mind-control expert. She could manipulate the thoughts, emotions and behaviors of others with her speech, actions and use of drugs. She was a skilled actress and chameleonic when in disguise. She seemed experienced with a handgun and use of biological weapons.
She seemed suffering from the Lima syndrome, in which abductors develop sympathy for their hostages.
Age of Apocalypse
An alternate version of "Scarlett McKenzie" appeared in the Age of Apocalypse titles, particularly "Factor X" #1-4 (1995). She was the singer of the Heaven bar owned by Angel/Warren Kenneth Worthington III. Her co-workers included the Bedlam brothers ( Terrence and Jesse Aaronson). The club was a neutral ground for humans and mutants. Scarlett was secretly the mistress of Havok.
Havok remembered how "Scarlett" had tried killing him when they first met. She claimed to love him but Alex made clear there was no room for emotions in their relationship. But he did confided in her about his plans of assassinating Cyclops. What he did not know was that his lover was an agent of the Human High Council. She was already trying to arrange her escape, following the arrest of fellow spy Karma.
She was right to worry. Karma was interrogated by the Shadow King, giving him information on "Scarlett"'s actual activities. She was soon arrested by her old friends, the Bedlam brothers. Angel refused to help her in any way. Scarlett was already suffering from nausea, worried that she might be pregnant.
"Scarlett" was interrogated by Havok himself. He was enraged at her betrayal, noting how he endangered his career by having a human lover. She admitted to have been a spy both before meeting him and before Angel hired her in the first place. It was not a recent thing. However something occurred out of schedule. She announced her pregnancy, terrifying Havok who noted there were laws against interbreeding. His career could be over due to this little fact.
A "Scarlett McKenzie" impostor appeared in " X-Factor" #112-114 (1995). Havok's memories of Scarlett, mostly buried since the Siege Perilous incident in " Uncanny X-Men" #251 (1989) resurfaced. Leaving him confused and wondering if he is talking to a ghost or a hallucination.
He found himself sharing a flight with her in Tokyo. He touched her hand but could not shake the feeling someone was messing with his mind. He went on a rampage on the streets of Tokyo. This "Scarlett" briefly encountered Polaris, with neither woman recognizing who the other was.
This Scarlett was reportedly created by the Sugar Man and was working with Fatale to capture Havok and bring him to Genosha. Fatale dismissed her as an amateur and escaped with Havok. Leaving Scarlett determined to relocate her target. The subplot was mentioned in #114 but never resolved. Fatale took Havok to the Dark Beast, not Sugar Man.
Several bios of Fatale give Scarlett McKenzie as one of her aliases but this not really confirmed in these issues. With the two characters arguing with each other on panel.