What or who is dagon?
Dagon was a canaanite god.
“What or who is dagon?”
It was an Amorite/Philistine god particularly fond of human sacrifice. Its mentioned a number of times in the OT. See, for example, Joshua 19.27.
Dagon was one of the many false gods of the OT. Here is one account, and remember that the assertion is that we follow this god:
1 Sam 5:2-7 : 2 Then they carried the ark into Dagon's temple and set it beside Dagon. 3 When the people of Ashdod rose early the next day, there was Dagon, fallen on his face on the ground before the ark of the Lord! They took Dagon and put him back in his place. 4 But the following morning when they rose, there was Dagon, fallen on his face on the ground before the ark of the Lord! His head and hands had been broken off and were lying on the threshold; only his body remained. 5 That is why to this day neither the priests of Dagon nor any others who enter Dagon's temple at Ashdod step on the threshold.
6 The Lord's hand was heavy upon the people of Ashdod and its vicinity; he brought devastation upon them and afflicted them with tumors. 7 When the men of Ashdod saw what was happening, they said, "The ark of the god of Israel must not stay here with us, because his hand is heavy upon us and upon Dagon our god."
Obviously, the assertion is that none of us are Christians.