History
The past of the cuckoos is a unknown , but it is believed that they are the cloned daughters of Emma Frost. The are allies of the Hellfire Club , they helped Emma Frost try to eliminate Charles Xavier, which made Jean Grey release the Phoenix's power and destroy the X-Mansion. A year later, they tried to trick a captured Jean into removing the mental barriers herself using illusions of Cyclops along with Emma's illusion of Charles. After this failed, Emma left to help the X-Men and then tried to harness the Phoenix's power for themselves by creating illusions of Jean Grey. Charles, Magneto, Quicksilver and Scarlet Witch attacked a young Jean, tricking her into releasing the Phoenix which consumed them and made them destroy the Sentinels and almost killing the X-Men, if Emma had not taken the Phoenix, removing the girls from the Phoenix's control and killing her. Strangely, the Cuckoos were still in their Phoenix Force costumes when released from the Phoenix's control.
Trivia
The Stepford Cuckoos are voiced by Tara Strong.