Here's why:
* He's the leader of the Titans: Luke is the main antagonist in the first few books of the Percy Jackson series. He leads the Titan army in their quest to overthrow the Olympian gods and take over the world.
* He was a camper: Luke was a camper at Camp Half-Blood, a former friend of Annabeth Chase and a student of Chiron. This makes his betrayal all the more shocking and devastating.
* His motives are complex: Luke is motivated by a deep hatred for the gods, stemming from his belief that they abandoned him and his mother. He also feels betrayed by Kronos, who promised him power and revenge but ultimately used him for his own ends.
While there are other betrayals within the series, Luke is considered the biggest and most impactful betrayal in the early books of the Percy Jackson series.