More than 25 years into an ever-changing acting career, Ms. Posey, 49, continues to embody the irrepressible energy she has brought to films like “Dazed and Confused,” “Waiting For Guffman” and “Party Girl.”

She unapologetically wears oversized, Elaine Stritch-style eyeglasses and carries Tic Tacs in a dispenser the shape and size of a giant Tic Tac. She shares her West Village apartment with Gracie, her 14-year-old bichon frisé-poodle-Maltese mix; her friends are fellow artists — actors, comedians, directors — and her tastes are eclectic. Her idea of a good movie, she said, would be something from “the Estonian film festival I saw 10 years ago.”

Like her best-known characters, Ms. Posey carries herself with a blithe spirit that conceals a cutting sense of humor. She spent a walk through her neighborhood on the lookout for starlings and blue jays, and when asked for the address of a restaurant she recommended, she answered: “I’m not going to tell you. I’m a practicing psychic and I want to see if you can read my mind.”

For Ms. Posey, playing Dr. Smith is an opportunity to cavort among the stars on a big-budget series and to put her unique stamp on a beloved cult-TV character.