Phoenix is a force in the 
Marvel Comics universe with extremely powerful 
psionic abilities. It occupied different hosts at different times, including 
Jean Grey and 
Rachel Summers. The power gained by the host was often offset by the exponential rise in the host's 
flakiness[?], which would frequently render the host useless when needed most, thus keeping the team from getting too powerful.
The character Jean Grey was introduced as a member of the X-Men in the early 1960s, and Rachel Summers was introduced as a member of the British-based superhero group Excalibur.
 
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