Who is Countess Canarine from Commodore Hornblower and what is their importance?

Hornblower first meets the Countess at a dinner party offered by the Czar. She has bold, dark eyes with an internal fire and spirit. The Countess initially finds Hornblower uninteresting but pleasant—only when the Czar personally addresses Hornblower in a positive way does the Countess re-evaluate him.

The Countess is married to His Excellency the Intendant of Livonia, and she is present at the beginning of the siege of Riga. Hornblower finds her presence awkward, and they spend several hours in close proximity, pretending to be nothing more than casual acquaintances.