All those who are from Chennai(a city in southern India) are pretty sure have known about St. Thomas.. Does not matter whether u r a christian or not.. St. Thomas mount, Santhome Church, Santhome Beach (St. Thomas should have become Santhome :-)). Yes you are right we all know mostly to that level, but do we know that St. Thomas is considered as one of the 12 Apostles of Jesus(remember last supper) and is called as Twin of Jesus. (May be because he looks like that.. or may be he is born to Mother Mary, not very clear in the sources I found).Check this here
He questioned Jesus on his resurection and said only when he is able to see him again he will believe in him.. But do you all know that his visit to India is still under lot of questions.. Even though widely accepted that he came to Malabar coast(Western Coust of india), to have reached as far as Chennai is still a question, as per this book. Hey guys, that book does have very outrageous views.. especially it states something on temples at Mylapore, which currently we can neither agree or disagree.. but for a view you can go through..
if you want to know more about St. Thomas in Chennai refer this article which was published in The Hindu some time ago..