Goliath was the most impressive warrior in the Philistine army. However, was Goliath a native Philistine? The evidence suggests that he probably was not.
In Numbers 13, Israel sends out spies to spy out the land of Canaan. Upon their return, all but Joshua and Caleb were shaking in their boots. Their chief complaint was that the people “are of great height” and that the Nephilim (the sons of Anak) were there (Num 13:32-33).
The phrase Nephilim is not used often, but in the context of Numbers 13, it is obviously used to refer to someone of great height. This is confirmed by the LXX and Latin translations of “giants.” Even in Genesis 6:4, the narrator tells us that Nephilim (giants) were on the earth in those days, and also after. What that means is that after God wiped out the earth with the flood, giants began to populate the earth again.
Now, if Goliath was indeed a giant, then the pertinent question is whether or not he was a son of Anak. Take note of Joshua 11:21–22:
And Joshua came at that time and cut off the Anakim from the hill country, from Hebron, from Debir, from Anab, and from all the hill country of Judah, and from all the hill country of Israel. Joshua devoted them to destruction with their cities. There was none of the Anakim left in the land of the people of Israel. Only in Gaza, in Gath, and in Ashdod did some remain.
During the conquest, Joshua and the people of Israel drove out the Anakim and the survivors fled to the land of the Philistines, specifically the cities of Gaza, Gath, and Ashdod. Where was Goliath from? From the city of Gath. Hence, it makes logical sense that Goliath was a descendant of the Anak, a Nephilim (a giant) in the eyes of the Israelites.
This also explains how Israel had to deal with other giants from the Philistines (2 Sam 21:16-22; 1 Chron 20:4-8). If the Anakim were dwelling with the Philistines who had given them refuge, they would be helping the Philistines fight their battles. This appears to be the case with Goliath and his fellow giants, who suffered at the hands of the Israelites being driven from their homes about 350 years earlier.