Sid Sawyer, Tom Sawyer's half-brother, shares a home with him under Aunt Polly's guardianship in St. Petersburg, Missouri. A quiet and obedient boy devoid of adventurous or troublesome inclinations, Sid forms a behavioral counterpoint to Tom's mischievous and rebellious spirit. He habitually observes Tom's activities, routinely reporting rule violations to Aunt Polly. Specific actions include exposing Tom's forbidden swimming through discrepancies in his shirt collar thread and revealing Tom's truancy. Sid's adherence to adult expectations garners him preferential treatment from Aunt Polly over Tom, fueling fraternal tension. Tom interprets Sid's conduct as deliberate antagonism, provoking retaliations like pelting Sid with mud clods after the collar-thread incident. Sid's role persistently highlights Tom's traits through opposition, sustaining a consistent pattern of conformity and tattling in their interactions.