Fire and Life Incarnate- from the back of Excalibur #1
Rachel Summers has one of the most interesting- yet mysterious- backgrounds of any Marvel heroes in the 80s. Now, of course, they're all trying to be interesting and more often than not end up more confusing than anything else. But Rachel, who was first seen in 1980 in the "Days of Future Past" X-Men story, is genuinely interesting. Although admittedly, still confusing. ;)
Rachel was born in the future of the X-Men, to Jean Grey and Scott Summers. However, this happy childhood was cut short by tragedy; in her timeline, the Brotherhood of Evil Mutants had assassinated a senator and anti-mutant hysteria now swept the nation. Because of her ancestry, Rachel was hunted as a mutant. Her parents and most everyone she loved was killed, and she was captured and used as a telepathic "hound" to hunt other mutants. Finally one day she broke free of her brainwashed state and attacked her captors. She injured one, Ahab, who had been controlling her. After that she was confined to the Mutant Concentration camps. There she befriended Kate Pryde, an older and unhappier version of Kitty, along with Kate's husband Piotr Rasputin (Colossus) and Magneto. She also fell in love with an adult Franklin Richards.
Desperate to save her world and her family, she and the other formed a plan to prevent the assassintion years ago from taking place. She used her temporal abilities (which were much stronger than her inherited telepathy) to project Kate's mind into the past and into the body of her younger counterpart. With Kate's help, the X-Men foiled the assassination, but that still wasn't enough to erase the ill effects of Rachel's timeline. Eventually Rachel lost everything she held dear, except Kate. She continued to send her mind into the past, but this proved fruitless. However, once when her spirit was meditating above the city, the Phoenix force that had once pretended to be Jean Grey found her and was struck by the similarities. It followed her back to the future, and there it spoke to Kate. They made a deal to get Rachel back to the past, where she would be safe. Kate and Rachel escaped from the concentration camp and broke into government headquarters, where Kate spoke the codewords she and the Phoenix force had agreed on: "Dark Phoenix". With that, Rachel's power was given an incredible jumpstart by the Phoenix force, and her entire body was propelled back into the past.
There, she joined the X-Men. Eventually they all found out who she was, except for Scott. Rachel made everyone promise not to tell him. She was heartbroken to discover that in this time, not only was Scott married to a woman who was not her mother, but her own mother was actually dead- meaning she could never exist! It took Rachel some time to adapt to this, but eventually she managed to stabilize and establish an identity for herself on the team. Her hostility towards Scott for marrying someone else was obviously still there, though, as she deliberately took a costume similar to the one Jean Grey-Phoenix had worn, and adopted the name of Phoenix for herself.
At this point, Phoenix was unaware of the Phoenix force inside of her. Her memories became more and more fragmented the more she used her psi-powers, and she eventually forgot all about her temporal manipulation powers. She grew more and more powerful, but when she decided to kill the energy vampire Selene, Wolverine had to stop her. He mortally wounded her and she was only kept alive by her telekinetic abilities. At this point she met Spiral, who tempted her to come to Mojo's world and be his slave. Phoenix went.
She was gone for about a year of our time, finally showing up again after escaping MojoWorld- but with creatures called Warwolves on her tail. She contacted the two remaining X-Men for their help, and got the welcome assistance of Captain Britain and Meggan as well. When she was out of danger, the five formed their team.
Throughout the team's adventures Phoenix's memories became more and more fragmented- something she discovered that she held in common with Meggan. Eventually she was forced to relinquish the Phoenix force to save the world, and it was at this point that she regained all of her memories. It turned out that Kate had requested that the Phoenix force stifled her memories, to save her pain. Once the Phoenix left her with a portion of her former power, she remembered her temporal abilities and decided to return to her own time. When she did so she was able to defeat the Sentinels once and for all, but gave up the chance to remain in her own time and returned to our present to stay with her friends- her family. That is where Davis's work on Excalibur ends, and it ends with a great finality and closure.