Bilbo Baggins gives Frodo the Mithril coat in J.R.R. Tolkien’s The Lord of the Rings.
Bilbo presents Frodo with the coat and an Elvish sword during Frodo’s stay in Rivendell. The mail was made by the Dwarves from mithril, a rare and exceptionally strong metal associated with Moria. Bilbo acquired it during the events connected with The Hobbit.
The coat protects Frodo during the quest and saves his life when the Orcs attack the Fellowship in Moria. Its value is enormous, but Bilbo treats it as a personal gift rather than merely a treasure.
Readers sometimes attribute the gift to Elrond because Frodo receives it in Rivendell. Elrond provides advice and hospitality there, but Bilbo is the character who gives Frodo the mithril coat.