Born to Harvey and Mimi Mitchum, Stew is assumed to be an only child. He harasses Lemony Snicket and his associates throughout the series. Dashiell Qwerty described him as a 'public nuisance'.
Who Could That Be at This Hour?
Stew is first introduced trying to slingshot birds in the Stain'd-by-the-Sea library, and upon being provoked by Lemony's remarks, he threatens to slingshot Lemony instead. Dashiell Qwerty shoos Stew away, apologizing for his behavior. When Lemony and Ellington Feint are dropped off at the lighthouse, Stew teases Lemony by sing a song about Ellington and Lemony kissing in a tree.
When Did You See Her Last?
Acting as a fake police siren to replace the non-existent police siren for his parents' police car on the way to Partial Foods, Stew teases Lemony again, calling him 'Lemon Drop' while remarking that the town has no room for idiots. In an identity parade following a honeydew melon theft, he, Lemony and a small file cabinet were required to wear the Stain'd-by-the-Sea Sea Stains sports caps as well as cardboard signs that indicated '1', 'B' and an image of a star. Polly Partial incorrectly identifies Stew as the thief and the officers are enraged. They claim that Stew doesn't eat fresh fruit or vegetables and Stew says that he doesn't like the taste of them.
Stew is later seen mocking Lemony about his 'security blanket,' the cloth covering the statue of the Bombinating Beast upon Ellington's arrest for fraud. He reveals to Lemony that he has 'a friend who is good with a knife,' making Lemony realise that he's not just a childish bully.
Shouldn't You Be in School?
When Lemony sneaks into the Wade Academy Stew attacks him, knocking him unconscious. Ellington rescues Lemony while Stew searches for help. Stew was known to patrol the halls of the academy at that time, and he is shown ordering the students around with Sharon Haines.
Stew threatens Lemony once again at the loading bay of Partial Foods, warning him about intervening in Hangfire's plan. He lets it slip that they would be burning Diceys Department Store next and is admonished by Hangfire. Stew is seen in the Stain'd-by-the-Sea library afterwards, threatening to burn Caviar: Salty Jewel of the Tasty Sea. When he tries to, the sprinkler system that Dashiell Qwerty installed soaks the books before they can be burnt. Attracting the attention of his parents and S. Theodora Markson next door, he blames the destruction of the library on Ellington, prompting her arrest for destruction of property.
At first, Stew is shown as a generic bully who derives pleasure in harming small animals and people. He is easily provoked by smart remarks, and has a rather short temper. In front of his parents, however, he acts well-behaved, well-mannered and seemingly cute, such as when he claims to want to befriend Lemony, acts angered at being distracted from giving himself a spelling test and crying to his parents about the 'liberry' being destroyed by water.
Stew's darker nature surfaces upon revealing his relation to Nurse Dander in the second book and then his full involvement in Hangfire's plan in the third book.