Who is Joab from A Tale of Three Kings and what is their importance?

Joab is one of the criminals who join David soon after he leaves Saul's kingdom. Joab is the only follower brave enough to stand up to David when it appears he has no plans for the future. Joab wants to know what David is going to do and how he intends to get all these people out of the mess they find themselves in. David does not like the question because he never agreed to be a leader to these people. However, David finds himself fighting for these people anyway. Many of these people, Joab included, become loyal citizens of David's kingdom later when he finds himself the king he never really wanted to be. Joab is still at David's side when Absalom comes to take away his kingdom. Joab questions David again. Joab wants David to fight Absalom and keep him from taking over the kingdom, but David refuses. David believes it is God's will that Absalom take over the kingdom and refuses to stand against God's will. Joab does not understand and watches in frustrated as David walks away from his kingdom.