There is a certain sadness in Mr. Frank hiding in the Annexe.  The character traits that he displays and represents are the same elements that are needed in a world where humanity and dignity have disappeared.  I believe that we see this throughout the diary.  Mr. Frank is the one who is able to keep everyone together in the challenges of living in the Annexe.  He has a general nature to him that brings community and solidarity to everyone.  He is the solitary force that allows everyone to feel safe and free from horrific fears of what is happening outside.  His ability to work with everyone is very surprising given how wealthy he was in his life before the hiding.  For example, Mrs. Frank displays an attitude of being uncomfortable and inconvenienced by life in the Annexe.  Mr. Frank does not display the same feelings, as he understands what is at stake and does his best to have others share his own understanding in grasping the intensity of the moment.  Mr. Frank's goodness is what ends up defining him the most in the narrative.  There is a certain hollowness when it is learned that he is the only one who survives.  The goodness of his character is one that is not to be shared with his family when the camps are liberated.