After the gods brought down the titans Zeus, Hades, and Poseidon had to decide who would rule where. Zeus ended up tricking Hades into ruling the Underworld alone in the darkness.
Hades was lonely until one day he saw the goddess Persephone. He instantly fell in love with her and went to Zeus to get help in pursuing her. Zeus agreed to help Hades in making her Queen of the Underworld.
Persephone was in the fields playing with the nymphs. Her mother, Demeter, was not there seeing as she was looking at the current harvest. She saw a flower and drifted away from the nymphs to look at it. When she went to it the ground split in half and she was sent straight to the Underworld.
Persephone did not want to live in the Underworld. Eventually Hades tricked Persephone into eating pomegranate seeds which gives Hades the right to bring her under during every winter. This devastated Demeter and she made winter a cold season while upset. She moved towards the mouth to the cave of the Underworld to be closer to her.
During the winter Persephone was forced to live with Hades. Like everyone else, she thought of him as cold-hearted seeing as he is God of the Dead and Wealth. During the harvest times she would return home to Demeter but often Hades would take her back early. Eventually she learned to love him and that even though he ruled the dead he wasn't cold-hearted after all.