Tonio Rossi functions as Marco Rossi's older brother in the family unit, residing with parents and Marco in Genoa, Italy, amid economic hardship. Due to severe financial strain prompting income-seeking decisions, the family dispatches Tonio to Milan for vocational training as a locomotive driver. This separation occurs before Marco's journey to find their mother. Tonio leaves his pet monkey, Amedeo, in Genoa with the family during his absence. Amedeo subsequently becomes Marco's companion, accompanying him throughout his travels across Latin America. Tonio's established presence stems from his familial role and departure for training. His actions and location motivate parts of Marco's experiences, primarily through Amedeo becoming Marco's companion. Tonio's character remains defined by his initial departure for Milan and his ownership connection to Amedeo.