Who is Uncle Hilary from One-Eyed Cat and what is their importance?

Uncle Hilary is Martha's brother. He lives in New York City and is a world-traveler. Hilary gives Ned a Daisy air rifle for his birthday, which upsets his father. Ned also has a collection souvenirs from his uncle's globe-trotting exploits. When Uncle Hilary comes to visit, the entire family becomes lighthearted and free. Uncle Hilary is ashamed of upsetting his brother-in-law by giving Ned the rifle.