Powers: Transmute flesh into organic steel, making him nearly invulnerable and providing super-strength
For most, the X-Men is an extended family. It figures that with few internal conflicts for Piotr within the X-Men, it's his biological family that causes so much trouble. Insanity runs through the Rasputin's, as does premature death. Faced with repeated tragedy, Colossus continues to maintain a positive outlook on life. He is the perfect contrast. In battle, he is the strongest X-Man, a brute force few can withstand. In private, he is a sensitive artist, deeply in love with Kitty Pryde.
Powers: Enhanced strength, incredible agility, prehensile feet
Hank is an original member of the X-Men and it would seem he'll be the very last to ever leave the mansion. He spends his days more often in the lab than in the trenches, but that makes him no less an X-Man. He is devoted to The Dream and firmly believes that man and mutant should live side by side as brothers. Hank has struggled with his animal form. He is, ironically, one of the most human of the X-Man, taking the opinions of others to heart. He shuts himself out from the world, often even from his teammates, to work in the lab and avoid the possibility of rejection for his looks. When the world can accept Henry McCoy, the X-Men will have succeeded in their mission.
Powers: Near total control of the weather, flight on gusts of wind
Few characters in the history of comics have seen as many in-continuity changes as Ororo Monroe. She is Goddess and warrior, friend and elitist, leader and loner. These contradictions are born from Ororo. They are not troubles merely sprung on by desperate writers. Storm is a character fighting who she once was (a frightened thief), who she thought she was (infallible goddess) and who she must become (an unwavering leader). Though Cyclops may be the default leader of the X-Men, in particular because of his allegiance to The Dream, Storm is the better choice to be in charge.
Powers: Enhanced agility, nightvision, teleportation, prehensile tail
Faith should have a prominent role in Xavier's Dream. However, almost all of the faith-based concerns fall on the shoulders of Nightcrawler. Deeply religious, Nightcrawler is feared and hated for his devilish appearance (and German accent). Oddly enough, he seems to receive more venom from religious zealots than most X-Men simply because of the way he looks. Religion is one of the few commonalities that could bring mutants and humans together and it is through his fait that Nightcrawler has stayed true to the X-Men for so long.
Powers: Telekinesis, Telepathy
Jean Grey is host to the most powerful entity in the universe. One of the original X-Men, Jean has become the symbol (and cruel joke) of death and rebirth among the mutant population. Partnered with the Phoenix Force, Jean has returned to the X-Men on several occasions. However, it's her first death that remains both memorable and significant to X-Men lore. Jean sacrificed herself, choosing to die as a human than live as a God. In a universe where self-worth is almost exclusive judged on power level, Jean held her humanity so dear she was willing to give up everything she loved. The strong-willed redhead is an integral part of the X-Men's legacy.