Peter Cookson, 76, an actor and writer best known in the theatrical world for his portrayal in 1947 of Morris Townsend, the fortune-seeking philanderer in “The Heiress.” Often working with his wife, actress Beatrice Straight, Cookson’s career as a stage actor was busiest in the 1940s both on and off Broadway. He went to New York for “The Heiress,” based on the Henry James novel “Washington Square,” after studying and performing at the Pasadena Playhouse. He appeared opposite and later married Straight, who portrayed the plain but wealthy protagonist in the play. In the 1950s he produced “The Innocents” and in 1953 was the male lead in the Cole Porter musical “Can-Can.” Most recently he had published a novel, “Henderson’s Head,” and a play, “Pigeons.” In 1984 his play “Unique Species” was staged to unflattering reviews at Los Angeles’ Pan Andreas Theatre. In Southfield, Mass., of bone cancer on Saturday.