Yes. Paul not only wrote 1st and 2nd Corinthians, but he wrote 13 books (epistles) of the New Testament, 14 if you consider him to be the author of Hebrews. In 8 of them he asserts himself to be an apostle of Jesus Christ "by the will of God". 1. Romans 1:1 2. I Corinthians 1:1, 9:1 3. II Corinthians 1:1 4. Galatians 1:1 5. Ephesians 1:1 6. Colossians 1:1 7. 1 Timothy 1:1 8. 2 Timothy 1:1 In fact, in I Corinthians 9:1, he claims to have seen Jesus Christ: "Am I not an apostle? Am I not free? Have I not seen Jesus Christ our Lord? Are you not my work in the Lord?" And in I Corinthians 15:8, after describing the resurrection of Jesus Christ and how He was seen of the apostles and followers, he add that "last of all He was seen by me also, as by one born out of due time."

TulsaDavid hit on most of the points, I'd just like to add some info from the other New Testament writers: Luke calls both Paul and Barnabas apostles in Acts: Acts 14:14 Which when the apostles, Barnabas and Paul, heard of, they rent their clothes, and ran in among the people, crying out, Peter, while not specifically calling him an apostle backs up Paul and his writings/authority, which is basically the same thing: 2 Peter 3:15 And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you; Therefore, to reject Paul means you must both reject Luke (and thus one of the Gospels and the book of Acts) as well as Peter (and thus both of his letters). Since Matthew, Mark, and John all supported Peter as an apostle in their Gospels and reliable, to reject him means you must reject them as well. Therefore, those rejecting Paul have essentially rejected almost the whole New Testament. I believe the only books remaining unrejected would be Hebrews and Jude, and a closer examination might reveal they might need to be as well.

Paul was an Apostle CHOSEN by God to preach to the Gentiles(because he was a well known DEVOUT JEW that persecuted Christians).. Jesus chose the 12 .... Paul confessed :he persecuted the church(Christ's body, the called out). Gal.1:13 he took great Zeal in doing so. (PERSECUTING CHRISTIANS)Ph.3:6 Thinking at the time he was doing right, he was a devout Jew, a blasphemer, persecutor, and very insolent man.1Ti.1:13 For these reasons, he considered himself the least of the Apostles, not worthy to be called an Apostle. 1Cor.15:9 WHAT WAS IT JESUS TOLD THEM ABOUT WHO WAS FIRST AMONG THEM, OR THE GREATEST? He told them " the one of you who thinks he is FIRST , shall be LAST! Even so, Paul's conversion, EXAMPLE, is God's wonderful way of showing HIS MERCY to ALL of us....

Matthew 15:5-10 HE was seen by Peter and later by the rest of "The Twelve." After that HE was seen by more than 500 Christian brothers at one time, most of whom are still alive, though some have died by now. Then James saw HIM and later all the apostles. Last of all I saw HIM too, long after the others, as though I had been born almost too late for this.For I am the least worthy of all the apostles, and I shouldn't even be called an apostle at all after the way I treated the church of God...

NO, absolutly not. John makes it very clear how to test spirits to see if they are of God. Anyone who does not believe that Jesus is flesh and blood person is not of God. Paul claimed that he was not given the revealation of the gospel from flesh and blood. Even his testimony confirms that He saw a light and heard a voice claiming to be jesus, but jesus told the disciples that if anyone says that he is in the dessert or a secret place not to believe them. You see The great king made a promise that he was going to prepare a place for us. This is why he told the disciples to go forth and preach the gospel,...he is busy!!!! Paul was only the first in a long line of false teachers who have used the pinciples attributed to Christ to spingboard their own personal agendas for prestige,power,and money...they will be judged.

SORRY TO THROW EVERYONE OFF BUT WHERE DOES THE JEHOVAH'S WITTNESS COME IN?

The term is principally applied to those disciples whom Jesus personally selected as a body of 12 appointed representatives. The names of the original 12 selected are given at Matthew 10:2-4; Mark 3:16-19, and Luke 6:13-16 Paul was modest. He called himself “the least of the apostles,” adding: “I am not fit to be called an apostle, because I persecuted the congregation of God.” (1 Corinthians 15:9) “The correct understanding of the wider application of the term “apostle” can help to clear away any apparent discrepancy between Acts 9:26, 27 and Galatians 1:17-19, when applied to the same occasion. The first account states that Paul, on arriving in Jerusalem, was led “to the apostles” by Barnabas. In the account in Galatians, however, Paul states that he visited with Peter and adds: “But I saw no one else of the apostles, only James the brother of the Lord.” James (not the original apostle James the son of Zebedee nor James the son of Alphaeus, but the half brother of Jesus) was evidently viewed as an “apostle” in the wider sense, namely, as “one sent forth” by the Jerusalem congregation. This would allow for the Acts account to use the title in the plural in saying that Paul was led “to the apostles” (that is, Peter and James)”.—Compare 1Co 15:5-7; Ga 2:9. “Matthias’ and Paul’s apostleships were both valid for the purpose for which those men were “sent forth,” yet when the apostle John saw the vision of the heavenly New Jerusalem in the Revelation (given about 96 C.E.) he saw only 12 foundation stones and on them inscribed “the twelve names of the twelve apostles of the Lamb.” (Re 21:14) The testimony of the Holy Scriptures is clear that the apostle Paul was never referred to as one of “the twelve.” Therefore, it logically follows that one of “the twelve names of the twelve apostles of the Lamb” inscribed on the foundation stones of the New Jerusalem is that of Matthias and not that of Paul. This means that the vision of the apostle John reflects the situation that existed at the start of the Christian congregation on the day of Pentecost in the year 33 C.E.” Source- The scriptures cited, please look them up in your own Bible, and the publication “Insight ion the Scriptures” Volume I

According to the Bible, he was.

Yes, and he was chosen to be an apostle ( messenger of the message) in a very special way. Paul call himself an apostle though abnormally born. He was given orders by Jesus Himself on the road to damascus and Paul was blinded for three days so that He would know what was happening to him was real and true.