Gladys Marchand (Vivienne Segal; 1897-1992) is the hidden main villainess from Alfred Hitchcock Presents' fifth season finale, "Hooked" (airdate September 25, 1960). She is the wealthy wife of Ray Marchand, who is younger than her.
The couple drove to a fishing camp, where Ray began smitten with Nyla Foster, a young student working at the camp--which is owned by her father. Gladys had known that Ray had dalliances with other women, and she teased him regarding his eye for Nyla, to the point where she threatened to cut him off financially. Ray and Nyla eventually become romantic with each other, and since he would be broke due to a divorce, Ray planned to kill Gladys during their next fishing trip. Gladys was surprised when Ray revealed his plans to go on the fishing boat with her, as she knows how much he dislikes fishing.
The episode's climax saw the couple on the boat together, with a packed basket full of sandwiches and beer. However, unbeknownst to Ray, Gladys had her own murderous plans for her husband, and as Ray was set to push his wife overboard, the evil Gladys bludgeoned her husband with a club and tossed him overboard, killing him. The final scenes showed Gladys returning to the dock alone and informing Nyla and her father about what happened, cryptically telling them that Ray "fainted" before he could attack her, and that he fell overboard--while claiming that her inability to swim kept her from saving him.
The villainess took out the weapon and thanked Nyla for giving it to her, revealing Nyla and her father as conspirators. It turned out that Gladys was in love with Nyla's father, and she stated that she planned to marry him--after a six month "mourning" period--with Nyla happily accepting Gladys as her future stepmother. As Hitchcock revealed in his closing narration, Gladys (along with Nyla and her father) was arrested (off-screen) for killing her husband.