'Apostle' in the Bible

Paul, called to be an Apostle of Christ Jesus through the will of God--and our brother Sosthenes:

Am I not free? Am I not an Apostle? Can it be denied that I have seen Jesus, our Lord? Are not you yourselves my work in the Lord?

If to other men I am not an Apostle, yet at any rate I am one to you; for your very existence as a Christian Church is the seal of my Apostleship.

For I am the least of the Apostles, and am not fit to be called an Apostle--because I persecuted the Church of God.