Who is Superintendent Battle from Cards on the Table and what is their importance?

Superintendent Battle is a representative of Scotland Yard, invited to Mr. Shaitana's dinner party. He gives the appearance of being rather wooden and unimaginative. This is strictly a pose. The man is a brilliant investigator, and very thorough. Once he discovers that the four individuals in the room with the dead Shaitana, he agrees to work with all four sleuths present that evening, despite the fact that he does not really agree with Mrs. Oliver's methods of confusing fact and fiction.