The disciple who was nominated against Joseph Barsabbas (see Joseph [in NT], No. 6) and chosen to fill the place of Judas. Of his antecedents the NT records nothing beyond the fact that he had been a disciple from the beginning of the Lord's ministry; and of his subsequent career it tells nothing whatsoever.
Tradition is more lavish of information. Matthias, it is said, had been one of the Seventy (cf. Lu 10:1), and he justified his election by evangelizing the savages of Ethiopia and writing two books