Ballos is the hidden ultimate antagonist of the game Cave Story, met during one of the difficult endings.
Backstory
Ballos is the creator of the Demon Crown. His niece (his sister Jenka's daughter) Misery forced him to create it. Unfortunately, she was quite rude and harshly demanding. Due to this, Ballos cursed and doomed her (and also Balrog, but we don't know how he got into this mess) to obey the one who wears it. In the Nicalis translation, Balrog refers to Jenka as "Auntie," thus implying that Balrog may be Ballos' son.
Ballos originally had a very peaceful life in the surface many years ago. He helped many people, who loved him in return. However, the jealously king captured him and tortured him non-stop, seeing it much extremely jealous to see Ballos using his magic to teach many people, until he went insane. Destroying his lovely kingdom in flames. He sadly killed his son and wife.
Jenka, Ballos' sister, imprisoned him in the Seal Chamber in the Mimiga island. For Jenka, killing her younger brother would be impossible.