The fancy version of the Kir (exact same cocktail but just use a dry white wine instead of champagne), the Kir Royale is a wonderful and fruity champagne cocktail. I recommend using as dry a champagne as possible because the creme de cassis is already really sweet and if you start off with a sweet champagne then it’s just a bit too much and you lose the other flavors. The dryer the wine the better.
The Kir is named after the Catholic priest Félix Kir, a Nazi resistance fighter in the Dijon region during WWII. Félix Kir is credited with helping around 5,000 POW escape during the course of the war. After the war ended he was elected mayor of Dijon, where he stayed for 23 years till his death in 1968.