Which Harry Potter novel introduced Luna Lovegood?

Harry Potter and the Order of the Phoenix introduced Luna Lovegood.

Luna first appears as a Ravenclaw student on the Hogwarts Express at the beginning of Harry’s fifth year. Her unusual beliefs, dreamy manner, and firm loyalty make her one of the series’ most recognizable supporting characters. She joins Dumbledore’s Army and later becomes an important ally in the fight against Voldemort.

Luna is the daughter of Xenophilius Lovegood, editor of the magazine The Quibbler. Her father’s unconventional journalism and Luna’s willingness to discuss ideas other students dismiss contribute to her distinctive characterization. Despite being mocked at school, she demonstrates courage and emotional insight.

The character did not appear in the earlier novels, including Harry Potter and the Goblet of Fire. Evanna Lynch played Luna in the film adaptations, beginning with Harry Potter and the Order of the Phoenix in 2007. The novel itself was published in 2003.