There are 13 Pauline Letters in the New Testament [A few of which are considered by Modern Scholars to be the first writings of the New Testament]: 

Books/When:
1. Romans (57 AD)
2. 1st Corinthians (55 AD)
3. 2nd Corinthians (56 AD)
4. Galatians (48-50 AD)
5. Ephesians (60-62)
6. Philippians (60-62)
7. Colossians (60-62 AD)
8. 1st Thessalonians (50 AD)
9. 2nd Thessalonians (51-52 AD)
10. 1st Timothy (62-66 AD)
11. 2nd Timothy (66-67 AD)
12. Titus (62-66 AD)
13. Philemon (60-62 AD)

Who:
13 New Testament letters are Attributed to Saul of Tarsus, who later became known as Paul the Apostle. He was a violent persecutor of Christians until he had a revelation of Christ on the road to Damascus, and then he subsequently became the most devout follower of Jesus, and became responsible for converting the most Gentiles to Christianity in the 1st Century. 
[*Modern scholars only attribute 7 of the 13 letters to Paul; the rest they believe to be forgeries]