Hadadezer was king of Zobah in Syria during the time David ruled Israel.
He ruled an area that stretched from the land of Ammon in the south to the Euphrates River in the east. Hadadezer tried to take back control of this region, but David fought him and won (2 Samuel 8:3–12; 1 Chronicles 18:3–10).
When the Syrians came to help Hadadezer, David defeated them too. He also took control of Damascus, a major city in Syria.
Later, David sent men to show kindness to Hanun, the new king of Ammon, after Hanun’s father Nahash died (2 Samuel 10). But Hanun treated David’s men badly. He humiliated them (verse 4).
After that, Ammon prepared for war and asked Syria to help them (2 Samuel 10:6). David sent Joab, his army commander, to fight the combined armies of Ammon and Syria. Joab defeated them (verses 15–19; see also 1 Chronicles 19:16, 19).
After this defeat, Hadadezer sent more troops from the area beyond the Euphrates River. The armies met at a place called Helam. David fought them there and won again. After this, Hadadezer asked for peace and agreed to pay tribute to Israel.