Glory (Buffy the Vampire Slayer)

Warning: Wikipedia contains spoilers.

Glory was a goddess from a hell dimension, over which she ruled, with two other gods. She soon became the most powerful of the three. Afraid that she would take control of their world, the other two began a war against her; Glory lost the war and was banished into our dimension, where she was forced to share a body with a child named Ben, created especially to hold her. She soon began to gain control over Ben for short periods of time, taking the form of a human female which possessed superhuman strength, but lacked many of Glory's other powers. A magical "amnesia" spell kept humans from learning that Glory and Ben were one and the same, even if she transformed right in front of them.

Glory came to Sunnydale looking for "the Key", a mystical item that would break down the walls between all dimensions, allowing Glorificus to return to reign in her own dimension. Use of the Key would also cause the destruction of all other dimensions, including the one Buffy and her friends inhabit. Glory was not aware of what form the Key had taken, however; all she knew was that the Slayer, Buffy, had been charged with protecting it. Glory surrounded herself with loyal minions, and began the quest to locate the key.

In order to maintain her sanity, Glory fed off of other humans by a process that Buffy and her friends referred to as "brain-sucking." The humans that she "devoured" in this way became incoherent and mentally unstable; Glory's arrival in Sunnydale was followed by an inexplicable increase in the number of mental patients. One of her unfortunate victims was Willow's girlfriend, Tara.

For her part, Buffy was not initially aware of the Key's nature either. It was eventually revealed that Buffy's sister Dawn was the Key, in human form. Glory soon discovered this fact, and managed to kidnap Dawn.

The Key could only be used at a certain time, and as that time drew near, the power that separated Glory from Ben dissolved. They still inhabited Ben's body separately, but their memories and personalities began to blur together. Glory's ability to occlude her kinship with Ben dissolved; Buffy and her friends soon discovered that in order to kill Glory, they must kill Ben.

Buffy attacked Glory with everything she had: the Dagon Sphere, the Hammer of Olaf, her identical robot twin (the "Buffy-bot"), and eventually a wrecking ball, commandeered by Xander. However, the final spell that would invoke the Key had already been started. Ultimately, Buffy jumped into the portal that was opening between dimensions, resulting in its closure and her own death.

Glory was left weakened, losing her hold on this reality, and returned to the form and mind of Ben. Buffy told him to get out of town and he agreed, but Giles knew that Glory would return and suffocated Ben. As Ben died, so did Glory.