Who is the first preacher to teach christianity?

Answer 1

Probably Peter:

Act 2:14 But Peter, standing up with the eleven, raised his voice and said to them, "Men of Judea and all who dwell in Jerusalem, let this be known to you, and heed my words. ..................

Act 2:32 This Jesus God has raised up, of which we are all witnesses.

Act 2:33 Therefore being exalted to the right hand of God, and having received from the Father the promise of the Holy Spirit, He poured out this which you now see and hear...................

Act 2:36 "Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ."

Act 2:37 Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, "Men and brethren, what shall we do?"

Act 2:38 Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit.