What role does Mr. Wingfield play in the Glass Menagerie?

Hey Everyone. I need help answering an essay question for my AP English Lit Class. I have no clue where to start. The prompt is:

Although he never makes a live appearence in they play, Mr. Wingfield is a major character in the Glass Menagerie. Discuss what role he plays and/or what impact he has on each of the other family members aa these years after his departure.

Thanks for all of your help.