Matthias was the apostle chosen after the Ascension to replace Judas. While he was chosen by lots, he had to fit the criteria outlined by St Peter: someone who had been a disciple from the very beginning, from his baptism by John until the Ascension. He must have been, directly or indirectly, a witness to the crucifixion and the resurrection of Jesus. That is all we know of Matthias from Scripture.
It is believed that he preached the Gospel for more than 30 years in Judea, Cappadocia, Egypt and Ethiopia. Tradition tells us that he was stoned to death in Colchis around the year 80, and there are claims to his relics in Trier in Germany and in Rome in Italy.