The following paragraph is taken from the "Catholic Almanac"

Thomas (Didymus): Notable for his initial incredulity regarding the Resurrection and his subsequent forthright confession of the divinity of Christ risen from the dead; according to legend, preached the Gospel in places from the Caspian Sea to the Persian Gulf and eventaully reached India where he was martyred near Madras; Thomas Christians trace their origin to him; in art, is depicted knelling before the risen Christ, or with a carpenter's rule and square; feast, July 3 (Roman Rite), Oct. 6 (Byzantine Rite).

There are many hundreds of interesting sources about St Thomas the Apostle on the Internet. One site that contains a beautiful homily by the Pope-doctor, St Gregory the Great, and ten other links is:

http://www.12apostlesofthecatholicchurch.com/

Thomas: also known as Judas Thomas Didymus or the "twin"