Violet is the 14-year-old eldest Baudelaire sibling. She possesses a brilliant mechanical mind and assumes a strong sense of responsibility toward her younger brother and sister following the tragic loss of their parents. Wise beyond her years, she observes adult behavior closely and relies on her inventive skills to build devices that help the orphans survive their dangerous circumstances.

Klaus is the 12-year-old middle Baudelaire sibling. His immense knowledge, gathered from reading countless books, provides critical information when the siblings encounter mysteries. He is more blunt and forceful than his older sister, often willing to dispense with adult pleasantries to speak the truth, though this causes the adults around him to dismiss his warnings.

Sunny is the youngest Baudelaire sibling. She is an infant with unusually advanced perception and four very sharp teeth. Though adults outside her family rarely understand her baby babble, her siblings comprehend her perfectly. She contributes to the family's survival through her willingness to bite hard objects and her ability to distract the oblivious adults around them.

Mr. Poe is a banker entrusted with managing the Baudelaire estate and finding suitable guardians for the orphans. He is well-intentioned but profoundly oblivious to danger, failing to notice obvious warning signs like snake-shaped hedges or flimsy disguises. He relies heavily on strict, literal proof and standard adult rules, making it incredibly difficult for the children to convince him of their ongoing peril.

Uncle Monty is an esteemed herpetologist and the Baudelaires' distant relative. Unlike their previous caretaker, he is genuinely kind and attentive to the children's individual interests. He lives in a large stone house filled with exotic reptiles and plans to take the orphans on a research expedition to Peru, offering them a brief glimpse of happiness and security.

Count Olaf is a ruthlessly greedy actor relentlessly pursuing the Baudelaire fortune. Having failed in his initial attempt to secure their inheritance, he infiltrates Uncle Monty's home disguised as a herpetology assistant named Stephano. He uses threats of violence to silence the children while maintaining an eager, helpful facade for the oblivious adults.

Lemony Snicket is the enigmatic narrator chronicling the tragic lives of the Baudelaire orphans. He frequently breaks the fourth wall to address the reader directly, offering vocabulary lessons, literary context, and dire warnings about the story's miserable events. Despite his melancholic digressions, he acts as a helpful guide who deeply respects the children's intelligence.

Dr. Lucafont is a medical professional who arrives at the estate during a crisis. He wears a white coat and possesses a strangely stiff hand. He confidently provides scientific explanations that perfectly align with Stephano's narrative of events, asserting his authority over the situation while ignoring the children's logical objections.

Gustav is Uncle Monty's previous herpetology assistant. His sudden, unexplained departure creates the job vacancy that leads to the arrival of the mysterious new assistant, Stephano, just days before the scheduled expedition to Peru.

Bruce is a pragmatic man associated with the Herpetological Society. He arrives at the estate late at night to manage the logistics of packing up and relocating the vast collection of snakes, showing little understanding of the animals' true worth or their former owner's brilliance.

The Incredibly Deadly Viper is a large, newly discovered species of snake residing in Uncle Monty's Reptile Room. Despite its terrifying name, the creature is completely harmless and affectionate, demonstrating the clear difference between fearsome appearances and gentle reality.