Danaus was the son of king Belus and Queen Anchinoe of Egypt and his brother was Aegyptus. The brothers were on bad terms, and to make peace Aegyptus wanted his 50 sons to marry Danaus's 50 daughters, the Danaids. The girls refused, and together with their father they fled to Argus, where Danaus became king. The 50 sons followed them there, and Danaus decided to let the marriages happen. He entrusted each daughter with a knife, and on their wedding night all but one murdered Aegyptus sons.
The disobedient, eldest daughter Hypermnestra was put in prison by her father, but freed later on. Artemis killed the Danaids for their crime and they were sent to the underworld, punished to forever try to fill jars with holes in them.
According to Apollodorus, these were the names of the 50 Danaids and their fiancees: