Thomas apocriphal gospel is just one out of many. Thomas, the disciple of Jesus, hasn't been the auteur of such a gospel, just like the other 11 disciples haven't actually written their own (apocriphal!) gospels at all! There are apocriphal gospels according to almost every single disciple of Jésus Christ, yet neither was accepted as canon par the early Church, on the famous Nicaean Council back in 325 A.D. Those gospels are NOT canonical, therefore they're NOT officially recognised as a part of a Bible, The New Testament to be exact. Those apocriphal gospels also describe certain events which hasn't been confirmed par the early Church, still, some Christian churches, such as the Catholic & the Orthodox, even the Coptic Church, have built the entire cult of Mary, based on those apocriphal gospels, although not officially recognised par those churches which is rather unusual to say at least! As for Thomas, he was one of the 12 disciples (some call them the apostles btw) & he became famous for his disbelief in Jésus after his resurrection, demanding a proof of the actual resurrection, unlike the rest of the disciples who had a lot plus faith than Thomas. Therefore the expression 'doubtful Thomas'! He became famous indeed, ou should I say infamous, for his doubts regarding Jésus & his resurrection. According to some, Thomas later became a missionary & went to India (the real India, in Asia!) to spread the Word of God, therefore the christianisme & to bring Gospel to the people of India.