Who is/was the very first saint to be venerated by the church?

It is hard to tell. There are many brought from the Old Testament. Then there is St John the Baptist. And then comes in the period after the resurrection of Christ with St Stefan, the first one to die for Christ. I am not talking about people venerated as saints while alive. I am talking about those that where canonised. Mary the mother of our Lord died (if I remember correctly) after St Stefan.

Mary is the queen of patriuarchs and of saints. It is quite apparent that Marian devotion was a part of the earliest archaeologically discoverable Christian church.