system
Given the following post, respond as if you're commenting on Reddit:
human
[Hey Arnold] Who is Mr. Smith? What is his job?

He seems to have some government ties and is elusive enough to only be noticed in the house in two episodes, despite living there.
gpt
He's there to spy on Arnold's Grandma and Grandpa. Did you ever stop to wonder how they know so much? How they seem to have a plethora of experiences outside of the ken of normal people? Grandma is a karate master, a former cop, a beekeeper, among other experiences. Grandpa is no different. They're very worldly people, despite giving off the aura of people who have never left the comfort of home.

In the forties, they were operatives for the OSS during the war. Grandpa's success at the Battle of the Bulge wasn't sheer luck, it was a OSS operation! Grandma was more of the infiltration type, hence why she knows skills like karate and is always coming up with new disguises. 

They were so successful that the post WWII paranoia/Red Scare left them on J. Edgar Hoover's watchlist. Mr. Smith is the agent ordered to watch them, but as tends to happen, bigger crises come up, larger issues need to be sorted, and everyone seems to have forgotten about Agent Steely and Agent Gertrude, as well as their watcher. But Smith files his reports every week. They just get lost in the bureaucracy.