The Charmed Ones

The Charmed Ones are a prophesied sisterhood of three (later four) witches who descend from the Warren line of witches. They are known as the most powerful witches ever to walk the Earth and are dedicated to protecting the innocent and ridding the world of evil.

Second incarnation
Soon after Prue's death, the remaining two sisters discovered that their mother had an affair with her Whitelighter, which led to the birth of their half-sister, Paige. With her help, Piper and Phoebe were able to use The Power of Three to fight evil again, and the Charmed Ones returned with a renewed set of members.

Third incarnation/Next Generation
Although it was stated that The Power of Three wouldn't be needed in a new no-evil future, years later the Elders were forced to recreate the team. Due to the honorable age of their former members and Paige's absence, the third generation now consists of the Charmed Ones' children, one from each of the previous member.

Unlike two previous incarnations, the current team doesn't consist of only female witches.

Fourth incarnation
After Wyatt Halliwell went rogue to protect his loved ones, he was locked in a so-called "magical prison" created by the Elders. His sister Melinda agreed to take his place, only to gain enough power to free her older brother and get rid of the influence of the Elders over their family in the future.