archetype is the original pattern or model from which copies are made, and by extension an instance so complete that it stands for its whole category.
The word does two jobs, and they can pull against each other. In its literal sense it names a source object — the master from which reproductions descend, the prototype later versions imitate. In its evaluative sense it names the defining specimen: the archetypal detective, the archetypal founding story. The first thing of a kind is rarely the best example of it, which is why the two senses sometimes point at different objects.
A third sense belongs to psychology. 📝Carl Jung used archetype for the inherited, universal patterns he argued surface across the myths and dreams of unrelated cultures — the shadow, the mother, the trickster. That usage remains contested as science and durable as vocabulary; most contemporary talk of character archetypes descends from Jung rather than from the literary tradition.
English took the word in the mid-sixteenth century from the Greek archetypon, "pattern" or "model," built from archein, "to begin," and typos, "impression" or "form." An archetype is not a stereotype, which is a flattened generalization applied to people rather than a source they derive from, and it is not a 📝mythos, which is the whole pattern of belief an archetype moves within.