Ahimaaz

(2.) The son and successor of Zadok in the office of high priest (1 Chr. 6:8, 53). On the occasion of the revolt of Absalom he remained faithful to David, and was of service to him in conveying to him tidings of the proceedings of Absalom in Jerusalem (2 Sam. 15:24-37; 17:15-21). He was swift of foot, and was the first to carry to David tidings of the defeat of Absalom, although he refrained, from delicacy of feeling, from telling him of his death (2 Sam. 18:19-33).

From Easton's Bible Dictionary (1897)