How did hades end up with the underworld as his realm?

Hades became the ruler of the Underworld after the Olympian gods, including himself, overthrew the Titans in a great war known as the Titanomachy. Following their victory, the three brothers—Zeus, Poseidon, and Hades—drew lots to divide the cosmos among themselves. Zeus received the sky, Poseidon the sea, and Hades was allotted the Underworld, where he governed the realm of the dead. This division solidified Hades' role as the god of the afterlife, overseeing the souls of the deceased.