Hans Castorp is the protagonist of The Magic Mountain: a young naval engineer from Hamburg who had not yet turned twenty-three when he went to Davos to visit his cousin for three weeks, and who ended up staying seven years at the sanatorium.
Orphaned of father and mother in childhood and, shortly after, of his grandfather, he was raised by his great-uncle, Consul Tienappel, in a house that gave him the habits of a Hamburg bourgeois, such as his taste for Maria Mancini cigars. The profession came from someone else's suggestion, not from vocation. The narrator calls him a "simple young man" and defines him less by what he is than by what the age did not give him: an answer to the question "What for?"
In the sanatorium, this lack leaves him open to everything. He falls in love with Clavdia Chauchat, listens for years to the debates of Settembrini and Naphta, studies anatomy on his own, and lets himself be fascinated by Peeperkorn. In the snowstorm of Chapter VI, he arrives alone at the sentence that would resolve the duel of the masters and, the same night, no longer quite understands it.
His arc is the passage from visitor to resident, and he decides none of the turning points: the body and the diagnosis decide that he stays, and the thunder of war decides that he goes down.