Eight days later, his disciples were inside again, and Thomas was with them. Although the doors were locked, Jesus came and stood among them and said, “Peace be with you." Then he said to Thomas, “Put your finger here, and see my hands; and put out your hand, and place it in my side. Do not disbelieve, but believe.” Thomas answered him, “My Lord and my God!” John 20:26-28 (ESV)
After Jesus' resurrection, even among the apostles, there were those who struggled or refused to believe He was alive. Thomas, in particular, earned himself the dubious honor of representing all doubters throughout history because of his unwillingness to believe.