While the plot doesn't exactly follow the exact description you gave, it shares many similarities:
* Gilgamesh, the protagonist, is a powerful king who experiences a profound loss - the death of his best friend Enkidu.
* Driven by grief and fear of his own mortality, he embarks on a perilous journey.
* He encounters a variety of supernatural beings and challenges, including the demon Humbaba, who guards the Cedar Forest, and the goddess Ishtar, who tries to seduce Gilgamesh.
* Ultimately, Gilgamesh's quest for immortality is unsuccessful, but he gains valuable wisdom and understanding about life and death.
While Gilgamesh doesn't explicitly rescue a wife from a demon-king, his journey shares the core elements of facing a powerful antagonist and overcoming challenges in pursuit of a loved one, even if it's not a romantic partner.