Thanos and Lanfeust share a common grandfather. Lanfeust’s grandfather impregnated the daughter of baron Averroes and Thanos is the grandchild of that short termed liason. Thanos (as Thanos) joins the conservatory of Eckmull, because he has magician abilities, the sameone as Lanfeust.
He is banned as a student by the sages of Eckmühl because they suspected he would use his powers to conquer and rule the planet. Thanos becomes a pirate and wears a mask as baron so nobody recognizes him. When he gets his hand on the sword of Knight Gold-Azure he becomes all powerfull and conquers Eckmühl. He rules as a ruthless tyrant, but is defeated by Lanfeust and imprissoned for life. Cixi had a short-lived relation with Thanos and became pregnant. She was able to abort the unborn child.
When Thanos is freed by Ice (Glace) he allies himself with Prince Delhuu and becomes his right hand in conquering the universe. Delhuu disposes of him when he is no longer needed, but absorbs his spirit. Thanos’ spirit succeeds in taking over Delhuu’s body and thus Thanos and Delhuu live in the same body. Thanos thus becomes prince Delhuu and ruler of the universe.
He looses the final batlle againts Lanfeust and is killed.