Adults automatically infer a person's social disposition and future behavior based on the many properties they observe about how they look and sound. The goal of the current study is to explore the developmental origins of this bias. We tested whether 12-month-old infants automatically infer a character's social disposition (e.g., whether they are likely to "help" or "hinder" another character's goal) based on the sounds and visual features those characters display. Infants were habituated to 2 characters, 1 that possessed more positive properties (e.g., a soft, fluffy appearance and a happy-sounding laugh) or more negative properties (e.g., a sharp, pointy appearance and a deep, ominous laugh). During test trials, we observed that infants looked longer at events that involved characters engaging in social actions toward another that were inconsistent rather than consistent with the valence of how they looked and sounded during habituation. Two control conditions support the interpretation that infants' responses were based on an inferred causal relationship between a character's features and its disposition rather than on some noncausal associations between the positive and negative valences of the characteristics and actions. Together, these studies suggest that infants are biased to connect an agent's audiovisual features to their social behavior.