Leaf is a member of the non-human race known as the Children of the Forest. She and her kin are responsible for the creation of the first White Walkers, thousands of years before the events of series.
When Bran Stark and his companions are attacked by wights as they approach the heart tree beyond the Wall that they have been searching for, they are saved by Leaf, who uses powerful magic in the form of explosive long-range fireballs to destroy the wights. During the attack, Leaf tells Meera Reed to leave her wounded brother Jojen to die, or else die with him. Leaf then uses her magic to destroy Jojen's body to prevent him from being reanimated as a wight. Leaf then tells the group to follow her into the cave at the base of the heart tree, explaining that the wights cannot follow them into the cave. As the group runs into the cave, Leaf tells them that she is one of the Children, before leading the group deep into the cave to finally meet the three-eyed raven.
Leaf sits nearby as Meera despondently regards the lands outside the Cave. When Meera rejects Bran's friendly overtures, Leaf tells Meera that her destiny is not over, as Bran still cannot defend himself in the real world and he will need Meera's help when he is ready to use his abilities outside the Cave.
Leaf is present when the three-eyed raven pulls Bran out of his vision of the Showdown at the Red Mountains. She appears concerned by the resulting argument between the Raven and Bran.
Bran has a vision of Leaf thousands of years in the past, in which she uses an obsidian dagger to convert a restrained man into the first White Walker. Upon waking up, he immediately confronts Leaf about the vision. Anticipating such a reaction, Leaf says that the Children of the Forest were at war, being slaughtered, their sacred trees cut down. She confirms that it was men with whom the Children were at war. Later, Leaf prepares the cave's defenses when Bran moves too quickly and attracts the attention of the Night King. She and the other Children fight wights with fire and the White Walkers with dragonglass, but her compatriots are killed one by one. Leaf flees with Meera, Hodor and Bran, but eventually sacrifices herself to give them more time to escape.
A Child of the Forest, Leaf looked after Meera, Hodor and Bran as the Stark boy learned from the Three-Eyed Raven. In a visit to the past, Bran witnessed Leaf creating tyhe first White Walker by pressing a dragonglass shared into a man's chest. She sacrificed her life so that Meera and Bran could escape from a wight attack.