Kong is a Colourpoint cat that lives in the same neighborhood as Francis .
In the movie, he is shown as a very unusual breed of large dimension despite the books description. He is a very tough, huge, dangerous, and fearsome type of feline who quickly show aggressive behavior toward strangers.
In the first novel, he's described as a Colorpoint cat. In Das Duell, he's said to be a "Persian Smoke": It is possible he's of a Persian breed but with smoke colorpoint coloration (Note: Colorpoint may or may be not considered a breed according the different cat registry). In the novel, he's described with blue eyes, differently from the movie which are gold yellow.
The first meeting with Francis is quite violent: Kong, being a ruler of the neighborhood, challenged the very presence of Francis and tauntingly refers to him as Bluebeard's gay lover.
Later, Kong attack Francis, alongside his minions Hermann & Hermann in the basement of Francis's home. There he even claim to be the responsible for the murdering (but Francis quickly realizes this is just a boast). During the fight, Francis manage to escape and while running away from garden to garden, he stumble upon the body of Solitaire.
As soon as Kong look Solitaire's disbowled body (with a gruesome show of the fetuses she carried inside), he's angered by pain. Solitaire is revealed to be his favourite female and supposed to be pregnant with his kittens.
Francis will realize how the she-cat actually cheated on Kong, because Claudandus killed her to prevent the birth of crossbreed cats sired by an unknown Felidae male.
After Solitaire's death, Kong stops showing interest in attacking Francis and focuses his anger on the killer (even though he never makes a true contribution to the investigation).
Kong appears again in Das Duel: he gathers a number of cats for a raid into the villa of Agatha (suspected to be the residence of the killer/s), however when Adrian face them and dismantle Francis' theories, Kong leave with the other cats.