As to his courage, he is absolutely lion-hearted where he can help or defend anyone else.Arthur Conan Doyle, "Three of Them I: A Chat About Children, Snakes, and Zebus," The Strand Magazine, April 1918
... it was discouraging to see her shrink in the face of her inadequacy rather than plunge ahead, lion-hearted, as if glory might yet be hers ...Tobi Tobias, "Winter's Tale," New York, January 18, 1993
Origin of lionhearted
We associate lionhearted and its shorter brother lionheart with King Richard I of England (1157-99). It is unknown whether King Richard could speak English (we know that he spoke French and Occitan, also called Provençal), but Richard’s nickname was not English; it was the French phrase Coeur de Lion. Lionhearted entered English in the 18th century; lionheart, the English translation of Coeur de Lion, was coined by Alfred Lord Tennyson in 1832.