Junko Enoshima

Execution time!

She hit the button with a hammer, and you fell under the floor.

Above all, Junko was deeply obsessed with despair, having found despair to be the most (and possibly the only) enjoyable emotion for her, whether it be inflicting despair unto others, or suffering from despair wholeheartedly. This made her extremely dangerous, as she wished to make the whole world feel absolute despair. However, this also often proved to be her biggest weakness, as she gave her opponents a "fair" chance to defeat her in order to make their despair all the greater if they fail, and happily welcomed her own despair if her plans failed.

Both Junko herself and the game's creators have confirmed that she truly has no reason to do the things she does other than despair itself, which makes her all the more dangerous and unable to be reasoned with. However it is hinted at in the anime that her analytical talent was what caused her to turn to despair, and that Hope's Peak was her first target because they see talent as hope, and use that talent for their own benefit, which drove Junko to take the talent they loved so much and use it for evil, which shows her in a more understandable light. It's also shown that under her amnesiac state, Junko doesn't show a thirst for despair or particularly strong hatred of boredom, implying that her constant case of forgetfulness had spared her from embracing despair again. However, the return of her memories reverted her to her former ways.

As the mastermind and leader of Ultimate Despair, Junko was shown to be highly intelligent, cunning, somewhat impulsive, extremely manipulative, and violent and cruel without remorse. She was a highly toxic individual, being both physically and mentally abusive to everyone around her. She manipulated people into falling madly in love with her and used their weaknesses, their despair, against them. Things like hope, peace, and happiness disgusted her, but she sometimes gave hope to others, only to turn it into greater despair later.