From BiblePortal Wikipedia

Fausset's Bible Dictionary [1]

Son of Rehob, king of Zobah. Helped by the Damascus Syrians (See Hadad ); driven by David beyond the river Euphrates ( 2 Samuel 8:3;  2 Samuel 8:5;  2 Samuel 10:6-9;  1 Chronicles 18:3;  1 Chronicles 19:7-19). After Joab's first repulse of Ammon and their Syrian allies Hadarezer, undaunted by defeat twice ( 2 Samuel 8:3;  2 Samuel 8:5), sent a host under the command of Shophach to assist his kinsmen of Maachah, Rehob, and Ishtob; David in person routed them completely at Helam; thus, the Syrian confederacy was overthrown, Hadarezer's subordinate princes submitted to David who dedicated to Jehovah the 1000 "shields" or "weapons ( Shelet ) of gold" taken in the first war; these were long known as king David's ( Song of Solomon 4:4;  2 Chronicles 23:9). (See Helam .)

Rezonof Hadarezer's retainers escaped, and with "bands" marauded the thinly-peopled district between the Jordan and the Euphrates ( 2 Kings 5:2;  1 Chronicles 5:18-22), then became master of Damascus, and as an "adversary" did "mischief" to Israel in Solomon's days ( 1 Kings 11:28-25). (See Rezon .) Edom invaded Israel during David's absence at the Euphrates; Psalm 44 by the sons of Korah alludes to this. Psalm 60 by David was composed after victory in part had been gained over Aram Naharaim (Syria of the two floods) and Aram (Syria) of Zobah the kingdom of Hadarezer, who had come to help his vassals of Mesopotamia, the region of the two rivers Tigris and Euphrates; after having conquered the two Syrias, Joab returned and smote Edom in the valley of Salt; Psalm 60 refers to the expedition subsequently undertaken to occupy Edom in revenge for Edom's invasion of Israel.

Smith's Bible Dictionary [2]

Hadare'zer. (Hadad'S Help). Son of Rehob,  2 Samuel 8:3, the king of the Aramite state of Zobah, who was pursued by David and defeated with great loss.  1 Chronicles 18:3-4. (B.C. 1035). After the first repulse of the Ammonites and their Syrian allies by Joab, Hadarezer sent his army to the assistance of his kindred the people of Maachah, Rehob and Ishtob.  1 Chronicles 19:16;  2 Samuel 10:15. Compare  2 Samuel 10:8.

Under the command of Shophach or Shobach, the captain of the host, they crossed the Euphrates, joined the other Syrians, and encamped at a place called Helam . David himself came from Jerusalem to take the command of the Israelite army. As on the former occasion, the route was complete.

Easton's Bible Dictionary [3]

 2 Samuel 8:3-12 2 Samuel 10

Hastings' Dictionary of the Bible [4]

HADAREZER . See Hadadezer.

Morrish Bible Dictionary [5]

See Hadadezer

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [6]

the form of the name of the town mentioned in the account of David's Syrian campaign, as given in 2 Samuel 10, and in all its occurrences in the Heb. text (as well as in both MSS. of the Sept. and in Josephus), except  2 Samuel 8:3-12.;  1 Kings 11:23, where it is more correctly called HADADEZER (See Hadadezer) (q.v.).