However, if we're looking for the character who undergoes the least amount of change, it would likely be Luke Castellan.
Here's why:
* He's the villain from the start: Luke's antagonistic nature and loyalty to Kronos are established early on. He doesn't experience a major internal struggle or shift in allegiance.
* He's focused on his goals: Luke is driven by his desire to bring about Kronos's return. He doesn't show signs of wavering in his commitment or questioning his actions.
* His character arc is simple: Unlike other characters, Luke's arc doesn't involve self-discovery or redemption. He remains a consistent, unwavering antagonist.
While other characters, like Annabeth and Grover, demonstrate significant growth and development, Luke embodies a more static presence, serving primarily as a foil to Percy's journey.