Frodo uses the name Underhill at Bree in J.R.R. Tolkien’s The Lord of the Rings. The alias is intended to conceal his identity while he travels away from the Shire with the One Ring.
At the Prancing Pony, Frodo is registered as Mr. Underhill. The name does not fully protect him, because his behavior and the interest of suspicious strangers draw attention. He also accidentally reveals his identity when he puts on the Ring during the gathering in the common room.
The use of Underhill reflects a broader pattern in Tolkien’s story: names can reveal ancestry, conceal identity, or signal a character’s changing role. Aragorn is known publicly as Strider during much of the early journey, while Gandalf has several names across different peoples and languages.
Underhill is not Frodo’s family name. Frodo’s surname is Baggins, and his family home is Bag End. The alias is a temporary travel name used during the dangerous passage from the Shire to Rivendell.