Marvel Girl: After training with Xavier's School for Gifted Youngsters, Jean Grey joined the X-Men under the codename 'Marvel Girl' and was helped by Professor X to develop her telepathic powers.
Phoenix Force: When trying to escape the Sentinels, Jean Grey's powers were unable to protect her from a solar radiation storm. The Phoenix Force - a cosmic entity of limitless power - duplicated her dying body and infused it with an element of her psyche. Believing this to be Jean, Phoenix/Grey joined the X-Men team.
Dark Phoenix: The criminal, Mastermind, mesmerised Jean to become the Black Queen of the Hellfire Club and ultimately turning her into the insane Dark Phoenix. Dark Phoenix battled the X-Men and inadvertently destroyed an inhabited planet. Unable to control the Dark Phoenix, Jean Grey committed suicide.
White Phoenix of the Crown: Upon the death of the host body, Jean's consciousness returned to her original body, which had been cocooned by the Phoenix. Jean assumed the name "Phoenix" and linked with the Phoenix Force. When Xorn - posing as Magneto - killed her, the Phoenix Force resurrected her to bond with her again. Jean Grey is now the "White Phoenix of the Crown", inhabiting a higher level of reality.