The Apostle Thomas, “called Didymus.”
I know who Thomas called Didymus was. Kolokotronis is saying (post 25) that Didymus is the source of the teaching about the Assumption of Mary.
I had thought it was Aquinas, so I searched some sources. I was wrong. Aquinas validated the belief, but he wasn’t the source, but neither, apparently, was Doubting Thomas. The Encyclopedia of Catholicism references a sixth century apocryphal text, Transitus Mariae. This text refers to several of the apostles, including Thomas, being present at Mary’s assumption, but the text was purportedly authored, not by Thomas, but by the Apostle John.
An English translation of Transitus Mariae is online. It is a fascinating read!
If there is another citation or link pointing to Thomas as the original source of the Assumption doctrine, I’d be interested in it for comparative purposes.
Many thanks to FReepers for bringing this up!