Callisto is the psychotic villainess whose main goal in life is to ruin Xena's.
Callisto claims to be a prodigy of Xena's past. She was born in a village called Cirra, and when she was still just a small girl Xena's army pillaged her village. And amid the chaos, a fire broke out and consumed Cirra, and most of it's innocent inhabitants. Among them was Callisto's family. Xena vowed never to kill women or children in battle, and was guilt ridden by the accident. But Callisto not only lost her family, but her sanity and compassion. She vowed revenge, and dedicated her life to learning Xena's tactics and weaknesses to someday kill everything dear in her life.
She starts out with mind games and treachery with her first appearance in the episode Callisto, in which she kills and rampages mercilessly, while telling any survivors that her name is Xena.
At the end, Xena defeats her in a showdown, and then stops her from killing herself. Callisto is then brought to jail.
In the next episode, Return of Callisto, she escapes from prison and seperates Gabrielle from her new husband, Perdicus. Causing Xena grief on Gabrielle's behalf, she persues her in a chariot race, in which they crash, and both fly into a pit of quick sand. Xena uses her whip to get to safety, and Callisto starts to beg to be saved, but Xena lets her sink.
She's brought back to life by Hera to kill Hercules. Hercules takes her somewhere where they find Golden Apples. She eats one and becomes immortal. Hercules then traps her there until Xena gets her out because she needs her help to defeat Velasca. Callisto gets Ambrosia from Velasca making her a goddess. She then gets trapped a whole boat load of times again, in lava and under rocks. Hope recruits her as a servant by helping her get revenge on Xena, then promising to fix her life, then give her oblivion because living forever with herself is too much.
Xena finally kills her with the Hinds Blood Dagger sending her to Hell instead of oblivion like she wanted. There, Mephistopheles sends her back to Earth as a super powered ghost to corrupt Xena and bring her away from the way of the warrior to corrupt her spirit and bring her to Hell. Callisto didn't succeed so she went back to Hell and became a demon.
Xena became an Archangel to help Heaven fight off the demons and to save Gabrielle. There she trades places with Callisto and gets rid of all of Callisto's evil, making her an angel. Callisto then helps Eli bring Xena and Gabrielle back to life after being crucified, and is reincarnated as Xena's baby Eve.
Powers and Abilities
As a Mortal
Callisto is a great swords expert, and is about the same strength as Xena. Her fighting skills, and reflexes are also on the same level as Xena where she can catch the chakram, and even use it, but not as good. She is also acrobatic, can jump and flip impressively. She also has an ability to sense things around her, but it isn't as sharp as Xena's. She is cunning and a good strategist, but can let her emotions get in the way.
As an Immortal
Callisto has all the same abilities she had as a mortal, but is unable to die or be harmed. She can feel pain though and be chopped into pieces.
As a Goddess
As a Goddess Callisto has all her abilities as a warrior, but is a little more wreckless. She is also immortal and unable to be harmed, no longer feeling pain. Her main god powers are fire and teleporting, but as a god she can do just about anything. She was also shown shooting lightning, regrowing limbs, shooting energy balls, using telekinesis, super strength, making an explosive energy blast from her body, and shapeshifting.
She was also given the power to time travel in Hercules by Hope, but only used it once. Her teleportation power seemed limited though so that she couldn't do it if she was encased in rock or lava.
As a Ghost
As a ghost, Mephistopheles granted her god-like powers again. With them she was unbreakable, super strong, and had super speed.
As a Demon
As a Demon, Callisto had her normal warrior abilities, but more ruthless and stronger. She also had wings that she used to fly, and had fangs and claws.
As an Angel
As an Angel Callisto was peaceful, and didn't hurt anyone. She could teleport, and fly. She also helped Eli in bringing Xena and Gabrielle back to life and heal. She could also make Xena pregnant, and put her soul into the unborn baby to be reincarnated. Since she's and Angel, she was also able to find the Dagger of Helios. She also glowed, but it's not really a super power.