In Avi's "The Man Who Was Poe", who did Mr. Dupin think was the devil?

Upon being introduced, the very confused Mr. Dupin (Edgar Allan Poe) begins to create his own opinions of the people around him.

Among a big group of very solid admirers, the last to be introduced by Mrs. Whitman was Mr. McFarlane, whose credentials included the recognition of being a local poet from Providence. Mr. McFarlane did not cause a good impression in Dupin, basically due to his extremely cheerful disposition, which caused Dupin to dislike him. Also, McFarlane was a sycophant whose words for Dupin/Poe were quite splendid:

But I am not so fortunate in glory or genius as the famous Mr. Poe.

This is where the narrator says that, although McFarlane was "bald and cheerful", Dupin still "took him for a devil". In fact, Dupin is, in general not happy with just about anybody he has met.