Mean; Strong, Serious, Determined. 

"Many years ago, Chara fell into the Underground and quickly became famous throughout the Kingdom as the antithesis of the human image Monster society had slowly mutated over the eons they spent isolated from their former conquerors. Though a bit troubled emotionally--implied by the child to be the result of trauma they endured on the Surface--Chara, if treated right, can become the most devoted and supportive friend one could possibly imagine. Rumor has it that, shortly before the second human fell and massacred figuratively half the Kingdom, they were beginning to hatch a plan with their adopted brother to free the Monsters from the Underground--a scheme which involved, concerningly, the voluntary sacrifice of their SOUL.

After their adopted parents were tragically murdered by the second human soon thereafter, Chara was perhaps understandably enraged and killed them, that drew the disapproval of known softy Crown Prince Asriel with their urging for revenge. They were surprisingly slow to back down from their violent proposal given their close relationship with "Azzy," and the exchange ended with him exiling himself to the Ruins of the old abandoned capital, leaving Chara as the de facto ruler of the Kingdom of Monsters.

They now live alone in the castle, withdrawn; going about their daily routine of practicing their machete technique, watching increasingly edgy anime, and binging on chocolate, really only showing themself to conduct Monarch business and improve their broken record impression with their hate campaign-esque speeches about the "Sins of Humanity."