Mariclare Costello, a lifelong member of The Actors Studio, passed away on April 17 in Brooklyn. According to a statement from her family, she was 90 years old. Costello was recognized for her role as teacher Rosemary Hunter in the CBS series 'The Waltons,' and she portrayed a hippie vampire character in the cult horror film 'Let's Scare Jessica to Death.'

Born in Illinois, Costello was a founding member of the Lincoln Center Repertory Company and had appeared on Broadway four times. One of those productions was the 1970 play 'Harvey,' featuring Jimmy Stewart and Helen Hayes in the lead roles. In 1974, she played the character's wife opposite Martin Sheen in ABC's Emmy-winning telefilm 'The Execution of Private Slovik.'

Costello made her mark in 15 episodes as Rosemary during the first five seasons (1972-77) of CBS's 'The Waltons.' She was the first person to read one of the stories written by John-Boy (Richard Thomas) and married Rev. Matthew Fordwick (John Ritter) in the season four premiere (September 1975). In a 2011 interview, Costello recalled the wonderful times she had with Richard Thomas and John Ritter.

From 1977 to 1978, she played the head of a family in the CBS drama 'The Fitzpatricks.' This series, which told the story of a family with four children living in Flint, Michigan, was limited to just 13 episodes. In the 1971 film 'Let's Scare Jessica to Death,' directed by John D. Hancock, Costello portrayed the vampire ghost Emily Bishop, who terrorizes her mentally unstable friend (Zohra Lampert). Her emergence from a lake in a wedding dress is perhaps her most unforgettable scene.

Mariclare Catherine Costello was born on February 3, 1936, in Peoria, Illinois. Her mother, Margaret, was the secretary to the Speaker of the Illinois House of Representatives in Peoria and Springfield, while her father, Dallas, was a construction engineer for the Illinois Department of Transportation. From 1977 until her death in 2013, she was married to actor Allan Arbus, known for his role as psychiatrist Maj. Sidney Freedman on 'M*A*S*H.' Allan Arbus passed away at the age of 95.