Matthias was the follower of Christ who was chosen by the remaining 11 apostles after Judas Iscariot's betrayal to replace Judas and restore their number to 12 (Acts 1: 21-6). He had been with Christ and the Twelve from the time of the Baptism to the Resurrection.
According to tradition, he undertook a peripatetic life, preaching Christ's word in various countries, but there is nothing more about his activities in the Bible.
His usual attribute is an axe or a halberd, supposedly the means of his martyrdom. He is the patron saint of coopers.