There are multiple versions of the english bible because there's different ways you can translate ancient languages into modern english. Some translations use a more word-for-word translation which preserves the text itself and some use a more though-for-thought form which helps to communicate the overall message of the text.
The King James Bible is a great milestone in the history of the english language, but it's no without laws. It was written 300 years before the discover of the dead sea scrolls, so it relied on the Textus Receptus for the New Testament, a Greek text compiled by Erasmus from a limited number of late Byzantine manuscripts and the Masoretic Text for the Old Testament. Our knowledge of ancient languages has advanced vastly since the 17th century, and the KJV just didn't have the access to this knowledge (which isn't their fault), so it can't really provide the older and sometimes more accurate readings of the Hebrew Bible that we can get from modern, english translations.