Mrs. Marcus is a character in It's A Mad Mad Mad Mad World, played by actress/singer Ethel Merman. She is the loudmouthed, overbearing mother-in-law of Russell Finch (Milton Berle) and one of many people engaged in a race to Santa Rosita Park, CA in hopes of finding a small fortune buried under "a big W". Mrs. Marcus is the mother of Emmeline Marcus and has an ally in her son, Sylvester. Sylvester oftentimes will defend his mother's honor over everyone else.

Mrs. Marcus is a loud mouth, often known for her nasty insults; her snobbishness and hitting everyone with her purse. In the end of the movie, she (along with Monica Crump and her daughter, Emmeline) storms down the hall of the prison (where all were taken for their actions in the movie), and once again begins to yell and scream at everyone, blaming everyone but herself for their troubles, until she slips on a banana peel, which causes everyone in the hospital ward to break out in hysterical laughter.