John was called Chrysostom (which means "Golden Mouth") because of his reported eloquence. He was originally a priest of Antioch known as an outstanding preacher to the extent that listeners were warned not to carry very much money with them when they went to hear him speak, since pickpockets found it easy to rob those who were too intent on his wisdom to notice.
Although John was content and popular in Antioch, he became so famous that the Empress at Constantinople decided that she must have him for her court preacher, so she had him kidnapped and brought to Constantinople and there made bishop.* This turned out to be a gross error for all involved as John's sermons against corruption in high places earned him powerful enemies (including the Empress), and he was sent into exile, where he died in the year 407.
In our Anglican/Episcopal tradition, he is known through his familiar prayer that adorns our prayer book's Office of Evening Prayer:
Almighty God, you have given us grace at this time with oneHis collect reads as follows:
accord to make our common supplication to you; and you
have promised through your well-beloved Son that when two
or three are gathered together in his Name you will be in the
midst of them: Fulfill now, O Lord, our desires and petitions
as may be best for us; granting us in this world knowledge of
your truth, and in the age to come life everlasting. Amen.
O God, you gave your servant John Chrysostom grace eloquently to proclaim your righteousness in the great congregation, and fearlessly to bear reproach for the honor of your Name: Mercifully grant to all bishops and pastors such excellence in preaching, and faithfulness in ministering your Word, that your people may be partakers with them of the glory that shall be revealed; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.
[*Yes, he had to be kidnapped to be made a bishop, so reluctant was he for the office. This may mean that he is the one person in Christian history who actually should have been a bishop.]