Michael "Mikey" McKenze is the younger brother of Marissa McKenze. He is a supporting character, and he used to only appear a little in the series, but since Sammy Keyes and the Cold Hard Cash, he has had a larger role than before and has appeared in all the books since then.
Like his sister, Marissa, Mikey hasn't spent much time with his workaholic parents. He then spent his own time eating junk food and watching goldfish at the pet store. At school, he didn't have friends, and kids would tease him about being overweight. They called him names like Chunky Monkey, Fatty McWide, Chubby Cheese, Blubber Butt, the Flab-o-Matic, Tub-o-Chub, and Lardo. At recess the other kids played a game called Jab the Flab where they poked him and ran.
In his debut, Mikey was described to have curly, black hair that never looked combed, even when it's just been combed. He's fat, and was short for someone even eight years old. In the later books, it was revealed by Marissa that he lost ten pounds, and he's not eight anymore, but in fourth grade.
Since the beginning the series, Mikey has been whiney. He had an addiction to junk food and goldfish. He even pretended to be sick on the first day of third grade to go stock up on junk food. He could be extremely bratty and impatient, claiming to be hungry or thirsty while on a walk with Marissa and Sammy. Because of his weight, Mikey would be teased at school, and while at Hudson's, he cried and told Hudson about how kids teased him and how he didn't want school to start again. Hudson had Mikey spend time at his house for "Hudson's Boot Camp", and they went on power walks, and he had Mikey stay more active. By Sammy Keyes and the Wedding Crasher, Mikey's love for junk food has since decreased, and he doesn't whine anymore. He even lost ten pounds. His relationship with Marissa is better, and they've grown closer. In Sammy Keyes and the Night of Skulls, Mikey went trick-or-treating with some new friends.
- Yolanda McKenze-mother
- Bob McKenze-father
- Marissa McKenze- older sister
- Brandon McKenze- older cousin
- Bruce McKenze-uncle
- Nob McKenze-aunt
- When Mikey was at amusement parks as a little kid, his mom had him on a dog leash to keep him close by.
- For Halloween, Mikey dressed up as Spy Guy.