This article contains spoilers. Read at your own risk.
Mr. Maxwell is Nikki and Brianna Maxwell's father. He is a bug exterminator for Westchester Country Day. He is described as not the sharpest knife in the box. He is married to Mrs. Maxwell and has a mother, Grandma Maxwell. Like his wife, his first name is never revealed throughout the entire series.
He is shown to be nice and loving but can also be extremely clumsy and awkward at times. He is slightly immature. Mr. Maxwell has a van for his bug extermination business and it has a roach on the top. Brianna calls him "Max the Roach". Nikki has put herself through many things to not ride anywhere important in it, but in Tales from a Not-So-Fabulous Life, MacKenzie saw her riding in it and uses this as a threat or for blackmail. Little does MacKenzie know, Brandon is okay with it. He had even texted to Nikki that he has been dying to ride her dad's van, making Nikki read it several times before bursting out laughing. Mr. Maxwell and his wife one time invited Brandon over for dinner in Nikki's blog but she becomes embarrassed when Mr. Maxwell talks to Brandon only about bugs and her mother kept telling her he's cute.
Mr. Maxwell is a very nice and amazing father to his children as well as being loved and well cared for.