Flowey is the first major character that the protagonist encounters in Undertale. Flowey serves as the main antagonist for the Neutral and True Pacifist routes and can be considered a deuteragonist for the Genocide Route. He provides an introduction to the mechanics of encounters by sharing "friendliness pellets," which are actually harmful bullets, revealing his philosophy of "KILL or BE KILLED." He serves as the final boss of the Neutral Route.

As a soulless flower, Flowey is neither human nor monster. Because he has no SOUL, he is unable to feel compassion or love, and primarily seeks enjoyment from an intricate and disturbing curiosity that stems from his ability to "reshape the world" by his determination.