Maxwell 'Max' Kirrin is the son of Julian and Brandine. His sibling is Tara. He is a member of the Famous 5: On the Case. He is an adrenaline junkie with a big appetite. Whenever there is a clue that involves food, he can recognize it by simply smelling the object. However, despite that Max loves food, he enjoys sports, such as mountain biking or skateboarding, which is why he doesn't any weight. He is not exactly the brightest member of the group. For example, whenever something is amiss, he will often assume that the culprits are aliens or monsters. However, he does have his smart moments. For example, in the episode "The Case of the Hot-Air Ba-Boom", when he discovered Mr. Ledwell's pocketknife, he noticed the handle is made of rhino horn.
Max is seen wearing a green t-shirt with an ocean wave on it, khaki shorts, and white shoes. His hair is somewhat blonde, but is not as blonde as Allie's hair. Like Jo, he has freckles on his face, but has fair skin. He is the tallest of the Famous Five.