Nathanael came together to Jesus and that he was among the disciples to whom the Saviour appeared after the resurrection on the shore of the nea of Galilee. The other Gospels never use the name of Nathanael, but after Philip they always mention Bartholomew.
Born at Cana, in Galilee, he was placed by Jesus among the twelve (Gospel) and he was a witness of the principal actions of Jesus upon the earth. "The first gift vouchsafed to the Church by the Holy Ghost," says St. Paul, "is the grace of the apostleship" (Epistle).
He preached the faith in Arabia Felix: according to certain traditions he was flayed alive. He is thus represented in the beautiful white marble statue by Cibo, in Milan Cathedral.
His relics are venerated at Rome, in the church of St. Bartholomew on an island formed by the Tiber. His name is mentioned in the Canon of the Mass among the apostles.
Let us joyfully celebrate the feast of St. Bartholomew who, in heaven, praises God among the glorious choir of the apostles (Alleluia), and let us ask of God to grant to His Church to love what he believed and to preach what he himself taught (Collect).
To me, Thy friends, O God, are made exceedingly honourable: their principality is exceedingly strengthened. * Lord, Thou hast proved me, and known me: Thou hast known my sitting down and my rising up.
(Psalm 138:17,1-2 from the Introit of Mass)
Omnipotens sempiterne Deus, qui hujus diei venerandam sanctamque laetitiam in beati Apostoli tui Bartholomaei festivitate tribuisti: da Ecclesiae tuae, quaesumus, et amare quod credidit, et praedicare quod docuit.
Almighty and everlasting God, who hast given us this day a reverent and holy joy in the feast of Thy blessed apostle Bartholomew; grant, we beseech Thee, unto Thy Church ever to love that which he believed and to preach that which he taught.
"Philip met Nathanael and said to him: The one of whom Moses has written in the law and whom the prophets have announced we have found: it is Jesus of Nazareth the son of Joseph. And Nathanael said to him: Can anything good come from Nazareth? Philip said to him: Come and see. Jesus saw Nathanael coming towards Him and said of him: That is a true Israelite in whom there is no guile. Nathanael said to Him: Whence knowest Thou me? Jesus answered: Before Philip called thee when thou wast under the fig-tree I saw thee. Nathanael replied: Rabbi. Thou art the Son of God. Thou art the King of Israel."
(St. John 1:46-49.)
From the Catholic Encyclopaedia: http://www.newadvent.org/cathen/02313c.htm