Saul’s servant - Josephus calls him one of Saul’s freedmen. The difference this would make in Ziba’s position would only be that instead of paying in the fruits of the confiscated land to David, he would have to pay them to Mephiboseth.
Related Commentaries of 2 Samuel 9:9
2 Samuel 9:9
9 Then the king called to Ziba, Saul's servant, and said unto him, I have given unto thy master's son all that pertained to Saul and to all his house.