here were actually 5 Marx Brothers. 1938: Front L-R:
Harpo, Chico, Groucho; Back L-R: Zeppo, Gummo

Milton "Gummo" Marx (October 21 or 23, 1892 or 1893[1] – April 21, 1977) was an American vaudeville performer and theatrical agent. He was the fourth-born of the Marx Brothers. Born in New York City, he worked with his brothers on the vaudeville circuit, but left acting when he was drafted into the U.S. Army during World War I, years before his four brothers (Groucho Marx, Harpo Marx, Chico Marx, and Zeppo Marx) began their film career

Marx was born in New York City. His parents were Sam Marx (called "Frenchie" throughout his life), and his wife, Minnie Schoenberg Marx. Minnie's brother was Al Schoenberg, who changed his name to Al Shean when he went into show business. He was half of Gallagher and Shean, a noted vaudeville act of the early 20th century. Marx's family was Jewish. His mother was from Dornum in East Frisia; and his father was a native of Alsace, and worked as a tailor.[2][3][4]

His military service began shortly before the Armistice, and he was therefore never sent overseas. After leaving the army, Gummo, who in an interview said he never liked being on stage, went into the raincoat business.[5] Later he joined with his brother Zeppo Marx and operated a theatrical agency. After that collaboration ended, Gummo represented his brother Groucho Marx and worked on the television show The Life of Riley, which he helped develop. He also represented other on-screen talent and a number of writers.

Gummo was well respected as a businessman. He rarely had contracts with those he represented, his philosophy being that, if they liked his work, they would continue to use him, and if not, they would seek representation elsewhere.[6]

Gummo was given his nickname because he had a tendency to be sneaky backstage, and creep up on others without them knowing (like a gumshoe). Another explanation cited by biographers and family members is that Milton, being the sickliest of the brothers, often wore rubber overshoes, also called "gumshoes," to protect himself from taking sick in inclement weather.

He married Helen von Tilzer on March 16, 1929. Their son, Robert, was born in 1930.[7]

Gummo died on April 21, 1977, at his home in Palm Springs, California from a cerebral hemorrhage following two strokes.[8] His death was never reported to Groucho, who by that time had become so ill and weak that it was thought the news would be of further detriment to his health. Groucho died four months later.

His grandsons are actors Gregg Marx, Chris Marx, and actor/producer Brett Marx, who as a child actor appeared as 'Jimmy Feldman' in 1976's comedy film The Bad News Bears.

When Richard J. Anobile asked Groucho in The Marx Bros. Scrapbook which brother to whom he was closest, Groucho replied. "Gummo. He's a nice man, and that's more than I can say for Zeppo."