Thomas was one of the twelve Apostles, who is referred to as Thomas the Twin (Didymus) in Saint John's Gospel (John 11:16, 20:24).
At the time of Christ's first appearance to his apostles after the Resurrection, Thomas was absent, and on being told that the risen Christ had visited them, he refused to believe it, unless he could touch the wounds on Christ's body. On his next appearance, Christ showed Thomas the wounds in his hands and bade him put his finger in the wound in his side. Cima depicted this event in 'The Incredulity of Saint Thomas' in the Collection (John 20: 24-29).
According to subsequent legend, Thomas also required evidence of the Virgin's Assumption, so she lowered her girdle (belt) to him. This episode was often represented in Tuscan art because the relic of the girdle was preserved in Prato in Tuscany.