St Matthias was, of course, the apostle selected to replace Judas.
Matthias was one of the seventy disciples of Jesus, and had been with Him from His baptism by John to the Ascension (Acts 1:21-22). Acts 1:15-26 relates that in the days following the Ascension, Peter proposed to the assembled brethren, who numbered one hundred and twenty, that they choose one to fill the place of the traitor Judas. Two disciples, Joseph, called Barsabas, and Matthias were selected, and lots were drawn, with the result in favour of Matthias, who thus became associated with the eleven Apostles.
Little more is known about him, and there are contradictory traditions concerning his subsequent ministry.
According to Nicephorus, Matthias first preached the Gospel in Judaea, then in Aethiopia (made out to be a synonym for the region of Colchis, now in modern-day Georgia) and was crucified in Colchis. A marker placed in the ruins of the Roman fortress at Gonio (Apsaros) in the modern Georgian region of Adjara claims that Matthias is buried at that site.
The Synopsis of Dorotheus offers another tradition: “Matthias preached the Gospel to barbarians and meat-eaters in the interior of Ethiopia, where the sea harbor of Hyssus is, at the mouth of the river Phasis. He died at Sebastopolis, and was buried there, near the Temple of the Sun."
An extant Coptic Acts of Andrew and Matthias, places his activity similarly in "the city of the cannibals" in Aethiopia.
Yet another tradition maintains that Matthias was stoned at Jerusalem by the Jews, and then beheaded.
And according to Hippolytus of Rome, Matthias died of old age in Jerusalem.