Martha Brewster is a fictional character from the play "Arsenic and Old Lace," written by Joseph Kesselring. She is portrayed as a sweet and caring elderly woman who lives in a Brooklyn home with her sister, Abby. Together, they engage in charitable acts, but their kindness takes a dark turn as they secretly poison lonely old men. In the play, Martha's character embodies the theme of appearances versus reality. While she seems like a gentle and loving person, her actions reveal a more sinister side. The character adds humor and complexity to the story, highlighting the contrast between her demeanor and her deeds.