Thomas was deeply committed to his master, yet he struggled with many doubts and questions. On the day He rose from the dead Jesus appeared to a group of disciples in a room. For some unknown reason, Thomas was not there (John 20:19-24). The disciples later told Thomas and Thomas told them that he would not believe unless he seen and put his fingers in the holes the nails made and put his hand into His side he would not believe (John 20:25). That's how Thomas got his nickname and it has stayed with him throughout history.
Thomas told the other disciples that he needed proof before he could believe Jesus had risen from the dead, he was being honest. Faith does not prohibit investigation. Eight days later the disciples met together again and this time Thomas was there. Jesus asked Thomas to touch His wounds (John 20:27). Jesus knew what Thomas needed to believe. From there He guided Thomas back to faith.