arella is the princess of the sub-atomic world of K'ai. Although outwardly primitive this world has remnants of long-forgotten high technology and sorcery. Its people are green-skinned and for the most part blonde haired, but otherwise human.
Jarella's city is threatened by a number of menaces ranging from attacks by the gigantic warthos (wart hog like beasts larger than elephants) to the armies of the Warlord Visus. The Hulk appears in K'ai during an attack of the warthos and drives the huge monsters away. When the people come out to greet him, the Hulk is startled. He notices that they are green-skinned, like him and that they welcome him rather than running away.
The Hulk is especially taken with the lovely and gentle Jarella. She leads him into the city and calls on her sorcerers to help the Hulk learn their language. The spell succeeds and also allows the human personality of Bruce Banner to emerge in the Hulk's body. The Hulk and Jarella fall in love, defeat Visus, and seem destined to live happily ever after. Unfortunately destiny in the form of a supervillain named Psyklop interferes and snatches the Hulk away from K'ai.
Jarella later returns several times, and is eventually transported to Earth after another confrontation with Psyklop. She is unique in the series in that she accepts the Hulk unconditionally. She comes to know Bruce Banner's mind in the Hulk's body but is equally accepting of the Hulk personality, or Banner's body. This idyllic love is tragically thwarted.
Jarella dies in The Incredible Hulk #205 due to saving a boy from being crushed under a falling building. The Hulk takes Jarella's body to the Gamma Base, but the doctors are unable to revive her. He rampages in search for his friend, the magician Doctor Strange, but the latter is also unable to restore her, and he finally accepts that Jarella is dead, while being comforted by the Valkyrie. In The Incredible Hulk #246, Captain Mar-Vell shrinks the Hulk so that he may return Jarella's body to K'ai for a proper burial. After being put to rest her spirit takes farewell by creating a single green flower.
Many years afterwards, during a Fantastic Four storyline featuring a delirious Hulk rampaging through Las Vegas, the latter howls Jarella's name, as one of the 3 greatest tragedies that he considers to have befallen him, along with the poisoning of his wife Betty Ross Banner, and the death of his friend Jim Wilson due to AIDS.