There is no such thing as a black cougar. Never been photographed, never been bred. The only ones that were "found" in the Southeast were identified incorrectly and were either margays or ocelots. The black panther is a JAGUAR. It is the black jaguar that was associated to death by the Choctaw.
There are no authenticated cases of truly melanistic cougars (pumas). Melanistic cougars have never been photographed or shot in the wild and none has ever been bred. Unconfirmed sightings, known as the "North American black panther", are currently attributed to errors in species identification by non-experts, and by the memetic exaggeration of size. Black panthers in the American Southeast feature prominently in Choctaw folklore where, along with the owl, they are often thought to symbolize Death.
In his Histoire Naturelle (1749), Georges-Louis Leclerc, Comte de Buffon, wrote of the "Black Cougar":