The Phoenix Force

The Phoenix Force is a cosmic entity conceived at the beginning of time and representing life itself. It frequently takes human form, spent decades in the pursuit of its one true host, which is as close as the Phoenix can come to having a physical body of its own. This led it to inadventently cause the deaths of seven children, six of which it would go on to raise and would become the superhero team known as The Ashes. The Phoenix's current host is Alcyone.

Early history
(This section from www.marvel.wikia.com)

The Phoenix Force is one of the oldest known cosmic entities, representing life that has not yet been born. The Phoenix Force is an immortal, indestructible, and mutable manifestation of the prime universal force of life. Born of the void between states of being, the Phoenix Force is a child of the universe. It is the nexus of all psionic energy which does, has, and ever will exist in all realities of the Omniverse, the Guardian of Creation, and a de-facto guardian of the M'Kraan Crystal. The Phoenix is among the most feared being in the entire universe - having the power to cut and regrow any part of the universe, as well as destroy it entirely, which is part of the Phoenix's purpose: "The Judgement of the Phoenix": to burn away what doesn't work. Recent interventions of the Phoenix suggest that "what doesn't work" is what has become stagnant instead of naturally evolving.

During its time as a sentient entity, it traveled the cosmos just like other cosmic beings. At first, the Phoenix Force was a formless mass of energy, but thousands of years ago, it came to Earth, and met a magician named Feron (who worshiped the legendary Phoenix), whose daydream-like visions prompted the Phoenix to adopt the firebird form it has today. Feron asked the Phoenix to help him by lending its energy to project a stone pillar (which resembled a lighthouse) across the multiverse. The pillar became the lighthouse base for the British superteam, Excalibur

Genetic manipulation and the search for a host
In the year 1972, the Phoenix Force neared Earth while travelling through the cosmos. It happened to hear the distraught prayer of a young Narcissa Black, who had just miscarried her first child with then-boyfriend Lucius Malfoy, who was unaware that she was pregnant. Something about the witch captured the attention of the Phoenix, which felt that someone near to Narcissa might be its one true avatar and genetic template. The Phoenix Force resurrected the child in the hope that he would prove to be its true host, but very shortly, Narcissa left Lucius after his friends assaulted her in the Leaky Cauldron. Narcissa was unaware that the child within her was alive again, or that the emotional toll the situation had taken on her was worsened by the manipulation of the Phoenix in an attempt to ensure that the child was born with mutant abilities. After this experimentation further weakened the child and after observing the atmosphere surrounding his mother, the Phoenix chose to let him die again and resurrect him elsewhere. The Phoenix took Shi’ar Empress-Majestrix Erezel Neramani as its host and adopted the child, whom it named Prometheus, as it had read in Lucius’s mind that he would have chosen this as the name of his firstborn son and the Phoenix wished to honor the boy’s biological parents. The Phoenix realized early-on that Prometheus was not its true host, but it felt indebted to him from taking him from his family, and so it raised him as its son in the guise of Erezel, as well as the Empress’s own children, Cal’syee, D’Ken, and Lilandra. It monitored the lives of Prometheus’s biological family back on Earth, and it sensed a change and returned to the planet to investigate. The Phoenix learned that Narcissa was pregnant again, though the child’s father was Augustus Rookwood. It sensed that the female child would have been born with mutant abilities and began to manipulate her biological structure to more perfectly suit a Phoenix avatar. The process resulted in the death of the child, Eurydice, who transitioned into the afterlife to serve as the Pure One, lighting the realm and living under the watchful eye of Death herself. Death refused to allow Eurydice to leave the tower in which she resided in the afterlife, and the Phoenix returned to Erezel’s home with the Shi’ar disappointed and believing it had lost its true avatar. It sensed another chance when, after resuming her relationship with Lucius, Narcissa became pregnant again. Narcissa’s natural difficulty carrying a child to term was worsened for a third time by the Phoenix’s tampering, and Narcissa and Lucius’s daughter did not survive. The Phoenix Force resurrected her with the Shi’ar, as it had done with Prometheus, and named the girl Alcyone, as Narcissa would have done. In 1978, when Alcyone was two years old and Prometheus six, the Phoenix was discovered. It fled, taking Prometheus and Alcyone and remaining in the form of Erezel, leaving the Shi’ar without an Empress and Cal’syee, D’Ken, and Lilandra without a mother. The Phoenix went about its galactic business, keeping order and maintaining the balance of life while raising the children, who believed Erezel to be their mother. Later in the year, the Phoenix returned to Earth to attempt to engineer its vessel once again, in the form of the now-married Lucius and Narcissa’s next daughter. The child, Veritas, succumbed to the same combination of poor health and genetic manipulation as her brother and sisters, and she was resurrected to be raised by the Phoenix alongside Prometheus and Alcyone. Their brother Poseidon would meet the same fate the following year. Deciding that it had taken enough from the Malfoys, the Phoenix raised the four as Erezel’s children and educated them on how to use their mutant abilities, though it taught them little about their inherent magical talents. It did not attempt to modify the next child, which allowed Draco to be carried to term and born with minimal complications to his parents. However, Erezel was not the Phoenix’s one true host, and it eventually grew desperate to find her. In 1984, it attempted the process again, hoping that it would be successful with at least one of the twins Narcissa carried. Instead, both were killed. The Phoenix resurrected them to live with the rest, and Nereus and Leda were the final children it would take. It trained all six to utilize their mutations, and eventually, the group took on the codename “The Ashes” to honour their “mother.” In January of 1996, the Phoenix Force sensed the telepathic cries for help of the mutant Jean Grey. It knew it would have to merge with Jean to save her and the X-Men, and so it left Erezel, sending her and the children back to live with the Shi’ar. Having raised them, Erezel cared for the six deeply, and with her blessing and that of her biological daughter, the current Empress-Majestrix Lilandra, the Ashes were assimilated into the Shi’ar Imperial Guard and the royal family. Cal’syee and D’Ken refuse to accept them, though Lilandra has grudgingly done so as per her mother’s wishes. The Phoenix Force granted Jean Grey her heart's desire: to save the lives of herself and the X-Men. It placed Jean in suspended animation at the bottom of Jamaica Bay to heal while the Phoenix created a duplicate of her body and took on her persona, joining the X-Men and resuming Jean's relationship with Scott Summers. The X-Men believed the Phoenix to be Jean. Thus, they were heartbroken when the woman who had continued to fight alongside them with her newly-quantified powers was brainwashed by the villain Mastermind and driven mad. She renamed herself Dark Phoenix and became an enemy of the X-Men. Dark Phoenix destroyed a star in the system governed by the Shi'ar, who already detested the being for robbing them of their Empress. The Shi'ar demanded Jean answer for her crimes, and they sentenced her to death. A battle took place on the moon between the Shi'ar the the X-Men, who fought for Jean's life. Lilandra ensured that her adopted siblings were not aware of the battle, as she did not trust them to side against the Phoenix. In the end, Phoenix killed herself in order to save the others. The Phoenix Force returned to the White Hot Room in order to rebuild itself and heal, and Jean returned to the X-Men after being found alive at the bottom of the Bay. She resumed her life where she left off, only to eventually have the Phoenix return to claim her, though she was unaware of this. It was severely weakened for a time after its regeneration and chose to lie dormant, and the Blackbird explosion that claimed the life of Shadowcat and injured the remaining X-Men depleted its power further. Jean awoke following the explosion to survey the wreckage and believe her teammates had all been killed, and her grief awakened the Phoenix. The entity demolished the surrounding area, and Jean was found lying unconscious in the crater by Minister for Magic Rufus Scrimgeour and the Auror Ted Tonks. She was held in a tank within the Department of Mysteries to be studied by the Department’s head, Andromeda Tonks, who attempted to speak to the unconscious Jean as she studied her mutant physiology. Though Jean was incapacitated, the Phoenix was aware of Andromeda, as well as the fact that she was the sister of Narcissa, who had become the Minister for Magic. With its current host unable to return to the stars, the Phoenix left Jean for the time to search out the Ashes. It took Alcyone as its host and led the six to Earth, deciding it was time for them to be reunited with their real parents.

Phoenix avatars
The following have served as hosts to the Phoenix Force since 1972: