Roddy McDowall, after missing the second "Apes" movies" because he was busy in London directing another film, returns now to the role of Cornelius, the young chimpanzee scientist. The assignment is McDowall's 37th feature film, the roster including such well-remembered items as "How Green Was My Valley," "My Friend Flicka," "Kidnapped," "The Longest Day" and the original "Planet of the Apes." He is; in addition, one of the best known and most highly regarded magazine photographers in the world, his work appearing in most major publications. Never married, McDowall has become a confidant of many of the western world's most celebrated political and theatrical figures.

Kim Hunter, playing Zira, the chimpanzee scientist for the third time, becomes a mother in "Escape From The Planet Of The Apes." The proud father is, of course, the aforementioned Mr. McDowall. Miss Hunter has ahs a most impressive and long-lived career on the Broadway stage and in films. In both media she starred in "A Streetcar Named Desire," winning an Oscar for her work in the screen version. Among her greatest accomplishment is her ability to humanize Zira, reflecting chic, charm and jolly good humor through the heavy makeup which transforms her own lovely features into the beguiling likeness of the lady ape.

Bradford Dillman is the Connecticut-educated son of a San Francisco stockbroker. After graduation from Yale, Dillman served in the US Marine Corps during the Korean War, later won a scholarship to London's Royal Academy of Dramatic Art, but declined it to work at the Theatre de Lys in Greenwich Village. He played Eugene O'Neill in the Pulitzer Prize play, "Long Day's Journey Into Night" and came to 20th Century-Fox in 1957 where he made a lasting impression in "Compulsion." Most recently he starred in "The Mephisto Waltz." Dillman is married to Suzy Parker, the beauteous, auburn-tressed model and actress.

Natalie Trundy, in private life the wife of producer Arthur P Jacobs, is a veteran of both Broadway and films. Her career was interrupted some years ago when she broke her back. Among her Broadway credits are "A Girl Can Tell," "By The Beautiful Sea," with Shirley Booth, and "Girls Of Summer" with Shelley Winters. In the current film she plays Stevie, assistant to Bradford Dillman.

Ricardo Motalban (Armondo, the circus owner) approaching the age of 50, feels he is just at the beginning of his career although he has been an actor many years. "I think it's good when large success does not come too early to an actor," he says. Nonetheless, by anyone else's standards, Montalban has been a huge success for a long time. In 1940s, he played "Tovarich" at Fairfax High School in Los Angeles, and 25 years later he starred in "The King and I" at the downtown Music Center, turning in a cyclonic yet sensitive performance so finely honed that all the critics raved. In between, he made many films. Born in Mexico, he came to Los Angeles at 17. He made Spanish-language pictures, was signed by MGM to co-star in "Fiesta" with Esther Williams. During the years that followed he was the Latin lover - or menace - in many movies. But Montalban is an actor of great power and talent. He appeared with Agnes Moorehead in "Don Juan in Hell" and did two years on Broadway in "Jamaica," the hit musical.