Nemesis was a Greek goddess whose job was to reward people when they did good things and punish them when they did something bad. She didn't always punish an evildoer right away. Sometimes she would wait years to punish someone, or she might even punish a child or grandchild for the wrongs of his or her ancestors. Over time, her name became a generic English term for an avenger and later, a rival, or for a punishment.