Abner was a great general who fought most of his life for a bad king. Though he introduced David to King Saul (1 Samuel 17:55-58) and commanded David during his early campaigns, Abner ultimately followed Saul’s orders and fought against David. During the years when David’s band of outlaws was roaming the hills, Abner led the hunt to track them down. Along the way he and David won mutual respect as honorable enemies.
Even after Saul died, Abner remained loyal to the forces arrayed against David. He installed Saul’s son as king (2 Samuel 2:8) and fought a long civil war against David, knowing David was the anointed king of Israel.
Abner was loyal to Saul’s son until accused of disloyalty. Saul’s son, Ish-Bosheth, saw Abner as a threat to the throne and finally said something about it — albeit in a round-about way. He switched sides and died by treachery. Shortly after Abner’s death, Ish-bosheth was assassinated as he slept (2 Samuel 4), and David became king of the reunited kingdoms (2 Samuel 5).
Abner was a great soldier with undying loyalty to his king. He had his faults like we all do (like taking loyalty to the extreme), but Israel needed more men like Abner.