Jowy was not born to either the Atreides or Blight families. His mother, Rosa, later married Marcel Atreides and he was brought into the wealthy Highland aristocratic Atreides family. He was badly treated by his stepfather and stepbrother, and most of his peers disliked him because his family was very rich, so he only found companionship in his best friends Riou and Nanami. He and Riou joined the Highland Army's Unicorn Brigade. However, he escaped to Jowston after the Unicorn Brigade was massacred by Luca Blight. He decided to destroy Highland from within after witnessing the power of Luca--and thus he murdered Anabelle in order to win Luca's trust. Slowly but surely Jowy gained power within Highland, and because of the marriage with Jillia, this became a certainty. However, after the death of Luca, the effect of the Black Sword rune started to rob Jowy of his life as he constantly needed that power to keep the Beast Rune at bay. In the end his army is defeated, and he fled L'Renouille without a word. After that he travels the world with Nanami and Riou.

(Source: Suikosource)