ZEPPO MARX was the quiet one, the straight man, and he never really fit into the Marx Brothers act. He never really wanted to - his mother made him do it - and he was only too happy when he could quit.

In fact, in one of his later reminiscences, Groucho said of Zeppo, "He was a character of no importance. He was a lousy actor and he got out as soon as he could. Zeppo didn't like acting and didn't want to be an actor but we had to have a fourth brother . . ."

Zeppo (Hebert) Marx is the last brother left.

Now 76, the "straight" brother lives quietly in a mobile home in California and spends his time golfing and deepsea fishing from his own boat.

He sounds a bit like Groucho on the phone, and though he is affable and cheery, he hasn't much to say about the more colorful episodes of his life - his multiples marriages, his gambling.

He says his social life is active and be still sees old buddies Bob Hope and Frank Sinatra (whose wife was once married to Zeppo).

"He had 10 times the women either Groucho or Chico had," says longtime Marx Brothers associated, screenwriter Joseph ("All About Eve") Mankiewicz. "He's a good guy and a good gambler and was very strong and muscular and handsome," Mankiewicz recalled. Mankiewicz's brother, Herbert, produced a number of the brothers' all-time popular films, and Groucho has taken credit for the discovery of the highly successful Joseph: Groucho hired him as a counselor at a boys' camp the Marx family ran in New York.

After Zeppo left the act (after participating in five films, including some of the funniest - "Coconuts," "Animal Crackers," "Monkey Business," "Horse Feathers" and "Duck Soup"), he was an inventor (of a still-sold watch that sounds an alarm at an irregular pulse), developed a manufacturing business tht he sold and, with brother Gummo, became a highly respected and successful actors' agent.

"We were always friends," Zeppo said of his zany siblings. "I just wanted to go into business."