The “fifth Marx brother” would be Zeppo if you’re going by birth order, or Gummo, in order of popularity (Gummo only did Vaudeville and did not appear in any of the movies). However, the title actually refers to actress Margaret Dumont. Dumont is best known, even by movie fans who don’t know her name, as the “straight woman” in seven Marx Brothers films. She joined them in The Cocoanuts (1929), Animal Crackers (1930), Duck Soup (1933), A Night at the Opera (1935), A Day at the Races (1937), At the Circus (1939), and The Big Store (1941). But she had quite a career outside of the Marx Brothers.

Dumont was born Daisy Juliette Baker in 1882 (although she gave her birth year as 1888 during her acting career). She spent several years of her childhood in Atlanta under the care of her godfather, “Uncle Remus” author Joel Chandler Harris. She trained as an actress and opera singer as a teenager, and chose Dumont as her stage name. She used Daisy, Marguerite, and Margaret as a first name before settling on Margaret. Dumont worked in serious stage plays and musicals in both the U.S. and Europe beginning in 1902, and appeared in Vaudeville shows where there was more opportunity for work. She received good reviews for her comedic timing and her singing voice. At 5’ 9”, she was considered statuesque among actresses of her time.

Dumont gave it all up in 1910 when she married sugar heir John Moller Jr. Apart from a small uncredited role in the silent movie A Tale of Two Cities in 1917, she did no acting during her marriage. Then Moller died in 1918. Dumont returned to the New York stage, where she rebuilt her reputation as a talented performer. She did not need the money; it was the love of her profession that had taken second place only to her husband in Dumont’s heart. She never remarried, but kept acting for the rest of her life.

In 1925, George S. Kaufman recruited her for a musical he had written for the Marx Brothers called The Cocoanuts. By then Dumont was 43 years old. She returned for the Broadway version of Animal Crackers in 1928. Shortly thereafter, both musicals were made into movies.

In the Marx Brothers films, Dumont played a society matron, usually a wealthy widow. During the Depression, this was a type of character that the audience loved to see humiliated, and it happened. At the same time, Dumont played the type sympathetically, because no matter how Groucho treated her, her characters obviously found him attractive, funny, and even sexy. Whereas the perfectly stereotyped society matron character would be constantly offended at the Marx Brothers antics, Dumont’s characters wavered between perfectly-timed embarrassment and full-on collaboration. Groucho simultaneously courted Dumont’s characters out of greed and opportunity and genuine attraction. The audience came to expect a romantic setup followed by a swift insult. From Duck Soup:

Rufus T. Firefly: Not that I care, but where is your husband?

Mrs. Teasdale: Why, he's dead.

Rufus T. Firefly: I bet he's just using that as an excuse.

Mrs. Teasdale: I was with him to the very end.

Rufus T. Firefly: No wonder he passed away.

Mrs. Teasdale: I held him in my arms and kissed him.

Rufus T. Firefly: Oh, I see, then it was murder. Will you marry me? Did he leave you any money? Answer the second question first.

And in another exchange:

Married. I can see you right now in the kitchen, bending over a hot stove. But I can't see the stove.

But Dumont did much more than Marx Brothers movies. She played opposite W.C. Fields, Laurel and Hardy, Abbott and Costello, Red Skelton, Jack Benny, and other comedians in a total of 57 films. She also appeared in television comedies. Dumont was typecast as the society matron, but seeing her in lesser-known films makes it clear that she was playing a role, because her onscreen persona differed depending on the demands of the character. Her final film role was in the 1964 movie What a Way to Go! in which she played the mother of Shirley MacLaine’s character.

Dumont won a Best Actress Award from the Screen Actors Guild in 1937 for the movie A Day at the Races. In accepting, she said, “I'm a straight lady, the best in Hollywood. There is an art to playing the straight role. You must build up your man, but never top him, never steal the laughs.”

Groucho Marx was often unkind in remarks about Dumont, insulting her offscreen as if he were continuing a story line. That may seem strange since they had so much onscreen chemistry, but there are several explanations offered by Stacia at She Blogged by Night: Groucho may have been jealous of her popularity. He may have internalized the oft-repeated idea that Dumont was only playing herself, a clueless society matron, in the movies. After all, Dumont never publicly refuted the idea, even though she was obviously a gifted actress and comedian. Or Groucho might have just been entrenched in his role as an insult comedian.

Groucho maintained that Dumont didn’t “get” his jokes, a story that had been told about Dumont for decades. Yet she played off those jokes masterfully, and was sometimes caught stifling a laugh even in the final cut. That could have been a case of Groucho finding a funny story and using it over and over, as humorists sometimes do. If he really thought so little of her talent, why would the Marx Brothers keep casting her in their movies over and over?

Margaret Dumont’s final appearance onstage was for the live TV series The Hollywood Palace in March of 1965, when she and Groucho recreated a scene from the movie Animal Crackers. She died of a heart attack only a few days later at the age of 82.