Alongside her brother Jimmy, Ann joined millionaire Simon Utrecht and pilot Mike Steel in an experiment to simulate the crash that gave the Fantastic Four their powers. Ann joined the group as she wished for more than merely fame, she desired great power. Aboard the unshielded spacecraft, the group located the cosmic storm area. Suddenly, they were bombarded with cosmic rays, and the turbulence caused Ann to stumble back into the life-support cylinders. Both her mask and the cylinders cracked, with a mixture of gases seeping into her lungs. The four were quickly rescued by Bruce Banner, who had witnessed the expedition. The ship crashed to Earth and the U-Foes emerged.
Now calling herself Vapor, Ann attacked Banner when he revealed he had been the one to return their spaceship. Soon, however, the U-Foes discovered that Banner was really the Incredible Hulk. After her teammates failed to defeat the Hulk, Vapor started to suffocate him, gloating as he was unable to hurt her physically. However, when Vector joined in the battle, he unintentionally deflected Vapor from the superhero and into her brother, X-Ray, causing Vapor's hydrogen form to light ablaze with fire. Her teammates attempted to save her, but she managed to regain her physical form and put out the fire herself. Before the U-Foes could continue their battle with the Hulk, they started to lose control over their new powers. Vapor's physical body reverted back to mist and her atoms started to dissipate. In a last ditch effort, Vapor attempted to help Vector, but his powers deflected her and scattered her to the wind.
Alongside her teammates, she has had encounters with heroes including Hulk, the Avengers, Spider-Man, Crossfire, Puma, Darkhawk, and Portal. During the Acts of Vengeance, Vapor attempted to kill the Scarlet Witch. Vapor and the other U-Foes were recently recruited to serve Norman Osborn in his scheming, and have since joined the Hood's Gang. This arrangement ended after Norman Osborn fell from power following his attack on Asgard.
Selected by Alpha Flight, Vapor and the U-Foes joined in a battle against the Immortal Hulk which ended disastrously. Afterwards, Vapor and her team were hired for an undisclosed job which led to a confrontation with the Spider-Men. Stealing an item at Empire State University, she and X-Ray performed a radioactive combo attack which hospitalized the original Spider-Man, but they were subsequently apprehended by the newer one. While in custody awaiting imprisonment, she was approached by May Parker who needed a biological sample of her to develop a cure for her newphew, Peter, who was a casualty of her fight with the Spider-Men. Coming to appreciate May's maternal empathy shown towards her, Ann agreed to help then gave the sample she needed, and the two pleasantly parted ways.
Vapor's body has been bombarded with cosmic rays far greater then that of the Invisible Woman, since then her brother X-Ray has once more bathed her in cosmic rays so as to achieve better control over her gas-like form.
Gaseous Form: Vapor's body is that of living gas(es). She is mostly invulnerable to physical harm, although she can still be harmed by unconventional attacks.
- Gaseous Form Manipulation: Vapor is capable of transforming her body into any type of naturally occurring gas, either a pure element or with complex compounds including mono-molecular mists. She has once accidentally melted the skin of her teammate Ironclad. She can only achieve a human state again temporarily.
- Flight: She can float and move through air molecules allowing her to fly, at speeds unknown.
Capable scientist in fields of Engineering and Physics.
She is vulnerable to any chemical interaction that would affect the chemical-form she is currently in. On one occasion, the Hulk defeated her by spraying her with oxygen while she had taken the form of hydrogen, turning her into water. While generally immune to physical harm, she could still be harmed by different types of energy, such as Storm's and Thor's winds and lightning, or the sonic booms the Hulk produces by clapping his hands together, and even X-Ray's radiation.
- Vapor is the older sister of X-Ray, much like Invisible Woman is the older sister of the Human Torch.
- 56 appearance(s) of Ann Darnell (Earth-616)
- 6 appearance(s) in handbook(s) of Ann Darnell (Earth-616)
- 9 minor appearance(s) of Ann Darnell (Earth-616)
- 26 image(s) of Ann Darnell (Earth-616)