Joab - The commander of David's army and one of his closest advisers.  However, he disobeyed David's command not to harm Absalom by killing him (see Absalom).  This may have been why David replaced him (II Samuel 19:13).  After Absalom's death, David mourned his son and Joab admonished him for it.

 

"The king covered his face and cried out with a loud voice, 'O my son Absalom, O Absalom, my son, my son!'  Then Joab came into the house of the king and said, 'Today you have covered with shame all your servants, who today have saved your life and the lives of your sons and daughters, the lives of your wives, and the lives of your concubines, by loving those who hate you, and by hating those who love you.  For you have shown today that princes and servants are nothing to you; for I know this day that if Absalom were alive and all of us were dead today, then you would be pleased.  Now therefore arise, go out and speak kindly to your servants, for I swear by the Lord, if you do not go out, surely not a man will pass the night with you, and this will be worse for you than all the evil that has come upon you from your youth until now." (II Samuel 19:4-7, NASB)

 

But upon King David's death, Joab sided with Adonijah over Solomon and was executed for his betrayal. (I Kings 2:28-34)