You may already know that in 1522 the first English translation of the Bible was the result of an order by King James of England, resulting in the King James Version of the Bible. The translators did their best to translate from the earliest manuscripts available to them, primarily a text called Textus Receptus.
What you may not know is that the translators expanded a passage in 1st John 5. This passage, now called the Comma Johanneum became a cornerstone argument for the Trinitarian position and a bedrock argument for and against the King James Version.
See for yourself (the comma is in italics):
KJV 1 John 5:7 For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. 8 And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.
NKJV 1 John 5:7 For there are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one. 8 And there are three that bear witness on earth: the Spirit, the water, and the blood; and these three agree as one.
NIV 1 John 5:7 For there are three that testify: 8 the Spirit, the water and the blood; and the three are in agreement.
Some Christians resist the removal of the Comma even in light of its obvious ommission from original scripts. Most modern translations do not contain the Comma Johanneum.