A `doubting Thomas’ is a sceptic; the expression is used to describe someone who demands proof before he believes or accepts anything.
Example: Balagopal is a real doubting Thomas. He wouldn’t believe that the new house was mine till I showed him the documents.
When St. Thomas was informed that Christ had risen from the dead, he refused to believe it. He demanded physical proof of Jesus’ resurrection. It was only when he saw Jesus with his own eyes and touched His wounds did he believe what he had been told. According to scholars, the expression began to be used in the late 19th century. The earlier expressions that were commonly used were `wavering Thomas’ and `unbelieving Thomas’.