Lynne Marie Stewart, the character actress known for her work on Pee-Wee’s Playhouse and It’s Always Sunny in Philadelphia, has died.

The actress “passed away peacefully after a short illness” at home in Los Angeles on Friday, her manager confirmed to Entertainment Weekly. She was 78.

Stewart was best known for her collaborations with Paul Reubens in a multitude of Pee-wee projects, playing Miss Yvonne and a number of other characters. She also was responsible for numerous hilarious scenes in It’s Always Sunny, in which she played the chaotic, off-the-walls neurotic mother of Charlie (Charlie Day) in 18 episodes. 

Day paid tribute to his on-screen mother on Instagram. “RIP TV mom,” he wrote. “Thanks for 20 years of laughs. You deserve a standing ovation.”

Elvira, a.k.a. Cassandra Peterson, who worked with Stewart in Elvira: Mistress of the Dark and The Elvira Show, also honored her former costar online. “My heart is breaking upon hearing the news of my dear friend @lynnestewart78 Lynne Stewart’s passing,” she wrote on Instagram. “One of the kindest, sweetest, funniest women who ever lived. The iconic Miss Yvonne of Pee-wee’s Playhouse: She’ll always be ‘the most beautiful woman in Puppetland.'”

Paul Feig, who worked with Stewart on Bridesmaids, also shared his memory of the actress on social media. “So sad. Lynne was the best,” he wrote. “I was such a fan of hers and it was such an honor to work with her in Bridesmaids. A truly wonderful hilarious person. You will be missed, Lynne.”

Born in Los Angeles in 1946, Stewart majored in Theatre Arts at L.A. City College alongside her lifelong friend, Cindy Williams of Laverne & Shirley fame. Stewart was an early member of the Groundlings, a seminal improv comedy troupe that also included Reubens, Kathy Griffin, and future Saturday Night Live cast members Phil Hartman and Jon Lovitz at the time.

Stewart’s first screen credit came with Jack Nicholson‘s 1971 directorial debut Drive, He Said. In 1973, she appeared in George Lucas‘ American Graffiti alongside Richard Dreyfuss, who her manager described as a “childhood friend.” The film was nominated for five Oscars, including Best Picture, and earned $115 million at the domestic box office, making it the third-highest-grossing movie of the year.

Stewart worked with Williams on several episodes of Laverne & Shirley, playing an assortment of side characters. She also provided the voice of Shirley (Williams’ character in the flagship series) on cartoon spinoffs like Laverne & Shirley in the Army and Mork & Mindy/Laverne & Shirley/Fonz Hour.

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The actress was a part of Reubens’ Pee-wee world from its earliest days at the Groundlings, playing a key role in the original The Pee-wee Herman Show stage show in 1981, which was further popularized by an HBO taping. She portrayed Miss Yvonne, “the Most Beautiful Woman in Puppetland” who was frequently entangled with many of the male characters in the playhouse. She reprised the role in Pee-wee’s Playhouse on CBS, the 1988 TV movie Christmas at Pee-wee’s Playhouse, and the 2010 stage production The Pee-wee Herman Show on Broadway.

Stewart also appeared in all three Pee-wee movies, though she did not play Miss Yvonne. Instead, in Pee-Wee’s Big Adventure, she played Mother Superior; in Big Top Pee-wee, she portrayed Zelda the bearded lady; and in Pee-wee’s Big Holiday, she appeared as Jimmy.

On the big screen, Stewart played supporting roles in massive films, including Bridesmaids (in which she played Maya Rudolph‘s mother), Clear and Present Danger with Harrison Ford, The Running Man with Arnold Schwarzenegger, and Children of a Lesser God with Marlee Matlin and William Hurt.

On television, Stewart appeared in episodes of MASH, The Golden Girls, The Jeffersons, Night Court, Hawaii Five-O, Arrested Development, Grey’s Anatomy, Curb Your Enthusiasm, and 2 Broke Girls. She also provided voice work in projects like Batman: The Animated Series, The Tick, Barnyard, and A Pup Named Scooby-Doo.

Stewart’s final project was The Dink, a movie with Ben Stiller, Mary Steenburgen, Jake Johnson, and Ed Harris that is currently in post-production.