Phoenix (comics)
There have been several characters published by Marvel Comics to use the alias of the Phoenix. The first one, Baron Zemo, only used that alias once; the later bearers of the identity are far more notable, and all are associated with the Phoenix Force.The Phoenix Force is a powerful extra-terrestrial entity which possesses mortals and amplifies their psychic abilities. Its known hosts have included Jean Grey and Rachel Summers, both members of the X-Men. The entity did not physically possess Jean Grey; instead, it created a second body identical to hers and through that body acted for her while she lay in a coma. However, the Phoenix was unable to adapt to its newfound humanity and was driven mad; as the Dark Phoenix, it destroyed a planet populated by sentient creatures and subsequently committed suicide. Jean Grey was later revealed to be alive, and later reassumed the name of the Phoenix after marrying Cyclops.
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Most recently, Jean began manifesting the attributes of the Phoenix Force, and despite this generally retained her self-control until her death at the hands of Magneto.