Identity: Royal Guard Captain:
Undyne is the leader of the Royal Guard, a group tasked with protecting the Underground and capturing any humans who fall into it. She takes this role very seriously, though her methods can be ruthless, especially on the Genocide route.
Goal: To kill Frisk or any human: Undyne harbors a deep-seated hatred for humanity, driven by the belief that humans are responsible for trapping monsters underground. She sees humans as the enemy and is determined to prevent them from escaping, believing this is essential for monsterkind's future.
Intro. Undertale is Waterfall, specifically the area where the protagonist is hiding in tall grass at the base of a cliff. Undyne, hearing rustling in the grass, aggressively investigates, foreshadowing her strong and confrontational nature.