Ophis

Ophis is a character & the former Bigger Bad from the Highschool DxD series. She is the founder & former leader of Khaos Brigade & was one of the most powerful dragons to have ever existed until being depowered in Heroic Oppai Dragon arc by Samael's curse, which gave birth to her clone Lilith.

Personality
Being born from darkness, Ophis rarely shows any signs of emotions, with a goal to get rid of Great Red out of the Dimensional Gap to obtain "silence". Issei describes her as an honest & pure dragon who is naive. Azazel indicates Ophis have changed because of her interaction with humanity, with a yet unexplained answer.

In a side-story, Ophis shows a somehow really rude yet accurate way to describe people.

Appearance
It is unknown what Ophis really looks like but she is shown to be a true shapeshifter being able to manipulate her appearance at will, such as her body shape & size or regardless of race, age or gender. Unlike most dragons in the series whom resemble the classical reptilian monsters seen in mythologies, Ophis is a human-shaped dragon.

Azazel once stated that Ophis once took the form of an old man before deciding to change it.

Her current appearance is that of a cute young girl with long black hair down under her hips wih gray eyes & an unseen pointy ears different from a normal human's covered by her hair. She also wears a provocative black Gothic Lolita dress which exposes her breasts, albeit with black cross-shaped tape covering her nipples.

Trivia

 * Ophis represents Infinity, Nothingness & Chaos.
 * In an original draft of Highschool DxD, she was intended to die after ressurecting Issei. As seen in the afterword of Volume 12, she was also not meant to be part of Issei's harem but after seeing her on the cover, they decided to turn her into a mascot character.
 * Ophis' name means "snake" in Greek, referring to her powers revolving around snakes & part of her basis full name.
 * Her nickname "Ouroboros Dragon" refers to Ouroboros ophis (Greek meaning tail-devouring snake), the Infinite Snake which first appeared in Egyptian & Indian Mythology, as well as its Norse counterpart Jomungadr.
 * It is theorized by Sona Sitri that the reason Ophis sticks so close to Issei is because she is "possessing" him, to the point that he "shoulders a karma that not God can purify".
 * She was called "Orphis" in the English version of the anime.