How did Hades become ruler of the underworld?

Answer 1

After Kronos was toppled, the 3 brothers, Zeus, Poseidon, and Hades drew lots to see who ruled what. Zeus won and became the king of the gods. He also gained control of the skies. Poseidon became ruler of the seas and Hades was stuck with the underworld.

He did not do much except see to it that everything went according to the rules. He made sure that the people of dead were sent to the right field. He was also the god of the hidden wealth.