Why is the Lord's Prayer different in the NIV and KJV? Why is Matthew 6:13 different in the NIV that some other translations?

NIV (the latest version, I think is 2010)


  And lead us not into temptation, but deliver us from the evil one.


KJV


  And lead us not into temptation, but deliver us from evil: For thine is the kingdom, and the power, and the glory, for ever. Amen.


I checked the Chinese translation it also has the equivalent of "For yours is the kingdom and power and glory, for ever. Amen."

So is the NIV different?
There are two differences here:


"from evil" (KJV) versus "from the evil one" (NIV)
"for thine is the kingdom..." in the KJV but not the NIV.


The first difference reflects an alternative translation choice for the Greek word "πονηροῦ". This might be in the masculine or the neuter gender - the word forms are the same. But there is a difference in meaning: if it's masculine, then it's referring to a specific individual who is evil, "the evil one", but if it's neuter, then it means non-personified "evil" in general. In the absence of any immediate grammatical clue, it's a matter of judgement which reading to choose. The NIV translators simply made a different call from those who translated the KJV.

The second difference reflects the fact that not all early source texts include this bit of the Lord's Prayer. In fact, there is a denominational distinction as well: the standard Catholic  version of the Lord's Prayer does not include it, but most Protestants do put it in. It is not present in the oldest manuscripts of Matthew, but there are versions that include it, so again it is a matter of judgement between the two sets of translators as to which text version is "better".