Namora was born in the kingdom of Atlantis, deep below the ocean. In her youth she was an adventurous young girl. She ventured too close to a shark and was bitten. The shark bite should have killed her but it left her unscathed. She soon came to realize that she was Atlantis' first mutant.
Years later, another mutant child of Atlantis stepped forward. Attuma used his mutant might to kill Queen Dorma and attempted to seize her throne. Namora attacked Attuma and saved the kingdom. The people of Atlantis chose Namora as their queen, and she rewarded their confidence in her with decades of peace.
The world above the ocean was far less stable. After watching the surface dwellers destroy each other over two world wars, Namora decided she could not allow humans to eventually encroach on her kingdom. She led a preemptive strike on the surface world but was halted by a mental summons from Charles Xavier. The two spoke and she was shocked at the man's compassion for all people.
Namora put off her invasion and offered her part-time services to Xavier and his X-Men, feeling an immediate kinship with these fellow mutants. If not for Magneto, a peaceful world may have been possible. Magneto's attack on the human populace led to all mutants being hunted down and incarcerated. Namora watched in horror as the surface world erupted into a genetic war. She decided to attack the surface world once again, beginning with those who attacked her genetic brethren.
Namora killed the officially sanctioned heroes of the surface world -- the Avengers -- and even hunted down the Fantastic Four, the one team to speak out against the treatment of mutants, for standing by while mutants were murdered. Namora became ruler of the planet and, remarkably, it became a better place.
Many years later, Namora was visited by the Timebroker and unhinged from time. It is unclear as to what the Timebroker informed her would happen, but it is obvious she is not convinced he has told her the truth.
So far, Namora has proved to be a difficult fit with the other Exiles. She attempted to sabotage her first mission with the team in the prime Marvel Universe by contacting Reed Richards and telling him the Exiles meant to tamper with the timestream. Eventually, things were cleared up but it led the other members to question her willingness to be a part of a team. Whether she will ever truly fit in as a part of the group and follow the Exiles' directive is unclear.