Wesley Nichols, often referred to as Big Guy or Big Kahuna by Nate Wright, is the principal of P.S. 38. He is rather obese (very similarly to Chad Applewhite) and is subject to continuous jokes by Nate, although he is very kind to him, nevertheless. Principal Nichols is shown to be rather fond of his food, and sometimes Nate catches him eating things like donuts, cinnabons, and chocolate bars and even popcorn. In Big Nate: In The Zone, when all the junk food is took out of P.S 38 to be replaced by healthy alternatives, such as rice cakes, soy nuts, dried fruit, and fiber bars as said by Chad Applewhite, it is Nate who finds soda and very unhealthy treats in Principal Nichol's office.
He once mentioned that he read a lot of comics when he was a kid, and that he had every "Archie" comic.
In Big Nate: In A Class By Himself, Nate body slammed into him while doing a race to the flagpole with Francis Pope and Teddy Ortiz, though Nichols had a reason to give Nate a detention, he said that it was his fault. Later, Nate got a detention during lunch for a "green bean incident". This was when he tried to set a world record for the most green beans eaten in the shortest amount of time. It is shown that he gets out of his office in the mornings only when it is getting painted. When they get together there are no noticeable problems between the two.
He appears to be African American or Latino American, and has a black mustache. He is noticeably overweight.
In the comic strip, Principal Nichols is mostly seen to be wearing a white shirt with black pants and a tie with a checkered coat. When the strip started being colored his tie colors would sometimes change as would his pants. He is also known to wear glasses.
- He has the third-highest rating in Nate's P.S. 38 ANGERGRAPH!, rated as 'furious weekly'.
- It is revealed in Big Nate: In The Zone that he has a niece named Noelle Nichols, that attends P.S. 38.
- Most days, he heats up a Cinnabon to eat, as said by Geraldine Shipulski, his secretary.
- Nate usually says he is "morbidly obese".
- He is usually pretty nice to Nate when he's not doing something bad.
- He is usually hit with the worst Prank Day pranks; once, Nate put Epoxy on his chair and it got stuck on his butt, another time, Nate managed to make his desk disappear, Nate making his car disappear from the parking lot, and, at one point, Nate even managed to make his car disappear. Nate even managed to hack into the PA system so that it would play Mr. Nichols singing karaoke (the song being "The Joker").
- His childhood dream was to be an astronaut, and Nate made fun of that.
- He buys a Butterfinger from the vending machine every morning.
- He has a cot in his office for "power naps". Nate does found this out surprisingly.