X. Barnaby Dinglebat is Jacob's next-door neighbour. He is a spy who works for CMIST (Canadian Ministry of Intrigue, Spying, and Tattling). He often performs spy missions with his hampster, Intrepid, and Jacob. Out of all the adults in the series, Mr. Dinglebat has the most time to spend with Jacob, and treats him as an equal.

A running gag throughout the series is that he often uses silly disguises, or ones that barely disquise him at all, and his overall clumsiness, such as the time he falls out of Jacob's bedroom window.