Who was Thomas's twin?

The sainted apostle "Doubting" Thomas is called Didymus, the Twin. **Indeed, Thomas also means Twin**. > Thomas, called **Didymus** / Θωμᾶς ὁ λεγόμενος **Δίδυμος** (John 11:16; 20:24; 21:2) There is no clear indication in the Bible of who his twin might have been, but [it seems that several extra-Biblical traditions exist](http://en.wikipedia.org/wiki/Thomas_the_Apostle) that try to fill in the gap. Can anyone run through the different possibilities, and their level of support and acceptance? It seems to me that since a lot of this comes from the NT Apocrypha, there's a greater than usual density of Internet rubbish around the topic. Thanks in advance to anyone who can wade through it, or find more reliable sources instead!