Apex was the child of a couple that desperately wanted a superhuman child. They ended up with Apex, who would spend half of their time as Tim and half as Katy. Their parents kept them a secret, which infuriated Katy. She trained herself to be as powerful as she could possibly be, and caused a car accident, telling her parents that Tim was dead after suppressing him. She was sent to Braddock Academy, where she was trained, all while her brother watched, powerless to do anything. This is the story that Tim relays to the others, but it is debatable whether or not it is accurate.
Apex was created by writer Dennis Hopeless and artist Kevin Walker. They first appeared in the story "Worse Things" in Avengers Arena #1 (Nov. 2013).
When Apex was kidnapped by Arcade and sent to Murderworld, Katy used her powers to take out the competition using Death Lockette to defeat Juston Seyfert and kill Darkhawk. She remained in the background, primarily acting at night or manipulating her classmates subtly. One spur of the moment dig at Kid Briton weakened his resolved and, when a confrontation was forced by Arcade's teleportation technology to answer for the results of her manipulation, her world crumbled as what she had planned fell to ruin.
She managed to escape, but the death of Kid Briton left the control she sought over others and her surroundings shattered. This allowed Tim to take control of their body. He explained things to the rest of the people in Murderworld. Their history of her control and suppression of him and so on. They take a vote on whether or not to execute him in order to get to Katy before she returns. The majority voted to allow them to live, but decide to tie Tim up and place him under guard. However, when Nico Minoru has her back turned, Katy takes control again and kills Juston.
In the aftermath, she took Juston's body and his Sentinel away with her, only to toss the body aside for reasons known only to her while explaining to Death Lockette that she is going to win this competition, no matter what. X-23 and Chase manage to track her down (the later by accident), but she uses the Sentinel to stonewall X-23's bold strategy of . . . rushing head first into the enemy, and then takes control of Chase, who now wore the Darkhawk armor.
Throwing X-23's unconscious body at the gathered survivors (whom she apparently believed to be dead at the time, but was not), she launched an all out assault with the Sentinel and Death Lockette at her side. Of the teens, only Nico Minoru could hold her own against the insane teen. She managed to slow Katy down and teleport the others to the other side of the island. However, Nico was brutally attacked and left for dead when Katy brought Chase in to attack her.
Katy then went on burning the island down, to flush out her targets.
But Nico was not dead, and came back with a vengeance. Apex held her own against the witch, but with a word she utterly demolished the remains of the Sentinel, and literally disarmed Death Lockette. Seeing the end once again, she goaded Nico into attacking her.
Nico buried her and Death Lockette alive, but she lived, and found herself nestled amongst the machinery used to control Murder World.
And Arcade's Morgue.
Powers and Abilities
Apex claimed initially that she could only fly, although not very fast. She also stated herself to be a great manipulator and can - as she says herself - talk people into almost anything.
This obfuscated her true ability. Technopathy. She has been seen puppeting both Death Lockette and Darkhawk with relative ease, which might stem from the fact that both are heavily integrated with advanced technologies that provide her with the catalyst needed to manipulate them. However, this has yet to be expanded upon, and her talents in manipulation could be far more potent than she lets on. She also seemed to have let her skills with these powers atrophy in order to build up the initial false persona. Her initial, assumed, attempt to control Juston Seyfert's Sentinel resulted in its near total destruction (and the destruction of its A.I.), and her first attempt to control Darkhawk managed only in ripping the gem from the hero's torso.
She shares her body with her brother, Tim, and each struggles to gain control of the body, though Katy seems to have had control long enough to remain the dominant persona. Whenever control shifts from Tim to Katy and vice-versa, their body changes in shape and biology from male to female, suggestion a limited form of shapeshifting.
Apex strives to control the world around her. If she can control things, she is calm and collected. However, her mental resistance breaks when she loses that control--be it of a situation or something else. If she sees she is outmatched, she rapidly adopts a defeatist attitude, which lead to her defeat at Nico's hands, and Tim to re-assert himself for the first time in years.