The black cat that appears in every episode of Trigun is called "Kuroneko Sama" (which means "Lord Black Cat". The cat is a female and was a creation for one of Yasuhiro Nightow's first mangas (Japanese comic books) and he has stated that the cat is female. Her alternate name is "Kuroneko Kukan" or "Black Cat Space". She also makes a cameo in the video game "Wild ARMs: 2nd Ignition".
Yasuhiro Nightow has gone on record to say that English is the language actually spoken on the Planet Gunsmoke.