Hades was the leader of the underworld and the dead a long side him was his dragon hound Cerberus. Although he had him Hades would get super lonely.
Hades realized that he needed a queen and had immediately thought of Persephone the most beautiful woman in the universe. She also happened to be his brothers daughter. Hades told Zeus and Zeus had agreed but had not told Demeter his wife.
Hades and Zeus made a plan to capture her through a fire portal when she was playing outside.
Persephone cried and cried over again demanding to go home but Hades refused and locked her up until she listened
Never, my queen
TAKE ME BACK, WAHWAHWAH
Eventually, Demeter Persephone's mother had found out what had happened to her and was psychotic she said she would never grow another tree and stop all agriculture until she gets her back.
Where is my daughter!
Zeus had decided a proposition between Hades and Demeter that he can have her for 6 months and Demeter can have her for 6 months. He sent Hermes to the underworld to negotiate.