Dagon was a god of the Philistines.
When finally the Philistines captured Samson, they offered a great sacrifice to Dagon. They brought him into the temple of Dagon, between two columns. They made fun of him, Samson then prayed to The LORD to have his strength one last time, which He granted. Samson made the temple collapse, killing all 3,000 Philistines in them with himself.
The Philistines captured the Ark of the Covenant and took it into Ashdod, their capital city, they put it in the temple of Dagon. The next morning, the statue of Dagon had fallen on his face before the ark, then God smote them with Emerods. So the Philistines decided to sent it to Gath where there, too, God smote them. Then the Ark was moved to Ekron, where God smote them again. Then the Philistine lords sent the Ark back to the Israel.