AceShowbiz - Mariclare Costello, known for her role as the devoted schoolteacher Rosemary Hunter on The Waltons, passed away on Friday, April 17, in Brooklyn. She was 90 years old, according to her family.

Mariclare Costello also gained recognition for her portrayal of a free-spirited hippie-turned-vampire in the 1971 cult horror film Let's Scare Jessica To Death. Beyond film and television, she had a significant stage career, appearing in nine Broadway productions during the 1960s.

Born on February 3, 1936, in Peoria, Illinois, Costello earned her master’s degree in theater and education from Catholic University. She was an original member of the Lincoln Center Repertory Company and maintained a lifetime membership with The Actors Studio.

After completing graduate school, Costello moved to New York City where she quickly found success in both Off Broadway and Broadway productions. Her Broadway debut was in 1964, starring opposite Jason Robards in Arthur Miller’s After the Fall. She went on to appear in several other notable plays including But For Whom Charlie (1964), The Changeling (1964), Tartuffe (1965), Danton’s Death (1965), The Country Wife (1965), Lovers and Other Strangers (1968), A Patriot for Me (1969), and Harvey (1970), where she performed alongside James Stewart and Helen Hayes.

Mariclare Costello was married to actor Allan Arbus, best known for his role in M*A*S*H, until his death in 2013. Her contributions to stage and screen mark a distinguished career spanning multiple decades, remembered fondly by fans and colleagues alike.