Mr. Jefferson is Rowley's father, and is far more shrill than Mr. Heffley. Mr. Jefferson is extremely rude and paranoid, not accepting any criticism from anyone if they dare give any type of criticism about him or his property. He is the strictest father in the book series so far. He will not let Rowley play any video games with the slightest bit of violence or fighting in it, as he sees them as things that could change Rowley into a different person. Mr. Jefferson thinks Greg is a "bad influence" on his son. It is also shown that Mr. Jefferson had a close bond with Rowley.
He shows little interest in sports until in Dog Days, where he is found playing tennis with Rowley and golf with a caddy. Greg says in his language: "Your-pa dad-pa smells-pa like-pa a woman-pa!" Greg is then forced to go home, and Greg questions how Rowley's father cracked his code.[8]
In Dog Days, it is revealed that Mr. Jefferson's first name is Robert.