Nergal is the god of death and destruction (mainly associated with the destruction by flames and sun). He rules the underworld together with his wife, Ereshkigal. His parents are Enlil and Ninlil, so he comes from a powerful family.
He demonstrates this power when he conquers the underworld, a feat that even Inanna herself could not accomplish. After he has insulted one of the sons of Ereshkigal, the other gods urge him to go pay his respects to the goddess in Kur. The goddess tries to lure him in the same trap as she did her sister, by stripping him of his power at each gate. Little did she know that Nergal would actually bring 14 demons with him, posting a duo of demons at each gate of hell.
When he finally gets to Ereskigal, she tries to kill him. He successfully defends himself and beats her in combat. Before delivering the killing blow, she asks him to marry her.
Whomever said romance is dead was right.