Question:

Who wrote the book of Revelation?

Answer:
John the Apostle wrote the book of Revelation.

Revelation 1:4 – “John to the seven churches which are in Asia: Grace be unto you, and peace, from Him which is, and which was, and which is to come; and from the seven Spirits which are before His throne.”

We know this is not John the Baptist because he was killed during the earthly lifetime of the Lord Jesus.  Read Matthew 14:1-12 for the account of John the Baptist’s murder.