Acrisius

Acrisius was a mythical king of Argos. He was the father of Danaë and thus maternal grandfather of Perseus. He was eventually killed by his grandson. His brother Proetus originally shared the kingship with him until Acrisius was forced to expel him. Proetus approached his father-in-law, King Iobates of Lycia, for an army but Acrisius made peace with his brother and gave him half the kingdom.

Prophecy
Acrisius received a prophecy he would be killed by his grandson. He locked his only daughter into a tower in Argos, away from men. However, Zeus, who lusted for Danae, turned into a golden shower and seduced her. She eventually gave birth to Perseus.

When Acrisius found out about the birth, he locked her and the child into a chest and pushed it out to sea, not wanting to be directly responsible for the death of his  unarmed daughter and her child. Zeus guided the chest onto the island of Seriphos, where she was greeted by Dictys, a humble fisherman and the king's brother.

Eventually, King Polydectes lusted for Danae and sent Perseus on a quest to kill Medusa, in order to have him out of the way and unable to protect his mother. Eventually, when Perseus returned, he participated in the Olympics, which Acrisius was attending. When Perseus threw the discus, it whirled up into the royal box and struck Acrisius on the head, killing him instantly.

Perseus, ashamed of this, traded the kingdom of Argos to his cousin and obtained the kingdom of Mycenae.