Rei Ayanami is a fictional character from the Neon Genesis Evangelion franchise. She is the First Child (referred as the First Children in the Japanese version), the pilot of Evangelion Unit-00 and one of the central characters.
At the beginning of the series, little is known about Rei, and her stoic personality puzzles her peers. As the series progresses, her personality evolves, and she becomes more involved with the people around her, particularly her classmate and fellow Eva pilot Shinji Ikari. In the concluding events of the storyline, the audience learns that Rei's mysterious origins tie into the story's resolution where its revealed that she is a clone of Shinji's mother Yui Ikari. Her role in this conclusion is not made clear in the TV series, but is one of the principal plot points of The End of Evangelion.
