It's no secret—Seinfeld is one of the most popular television series ever. For the better part of the ‘90s, millions of people tuned in each week to get a glimpse into the life of four zany friends living in New York City. Perhaps just as beloved as Jerry, George, Elaine, and Kramer, though, was the rotating door of guest stars, which spanned already-famous performers to ones who were at the very beginning of their careers.

From a modern-day superstar who got their start on the buzzy show to a huge ‘90s actress who played one of Jerry’s love interests, here are 9 celebrities you didn’t know guest starred on Seinfeld. A few may surprise you.

Former Mets first baseman Keith Hernandez played himself in not one but two Seinfeld episodes. Jerry Seinfeld has shared that one of Hernandez’s episodes, “The Boyfriend,” is his favorite episode from the show.

Raquel Welch, the sultry screen star who acted in dozens of films over the years, appeared in a 1997 episode titled “The Summer of George.” Welch played a dramatic version of herself, who gets fired (by Kramer, no less) from a musical because she doesn’t want to move her arms while tap dancing.

Award-winning actress Marisa Tomei also made an appearance on the show as herself. "I was very excited to be part of something that was so treasured and had made me laugh so much over the years," Tomei told Insider years later. "It was really a thrill.”

Years before Entourage, a 20-something-year-old Jeremy Piven had a small role on Seinfeld. He played Michael Barth, better known as “TV George,” in the 1993 two-part season finale “The Pilot.”

You may be familiar with Courteney Cox for her starring role in another popular ‘90s show, Friends, but you may not know that while filming its first season, she also appeared on Seinfeld.

Starting in 1997, Breaking Bad star Bryan Cranston took on the recurring role of Tim Whatley, a dentist (and Elaine’s brief romantic interest) that appeared in five episodes. “The audition process for Seinfeld was great,” the actor told GQ in a recent interview. “I did it first for the casting director, Meg Liberman, and for the callback, Jerry was in the room.”

Before her White Lotus fame, then-budding actress Jennifer Coolidge appeared on Seinfeld as Jerry’s girlfriend, a professional masseuse named Jodi. Her small role on the show was her first credited television appearance.

Comedian Kathy Griffin got some Seinfeld screen time when she appeared in two episodes: “The Doll” and “The Cartoon.” Interestingly enough, the second episode was inspired by real-life: As the story goes, Griffin criticized Jerry while performing on an HBO comedy special, saying that he was rude to her. Jerry, in response, mailed her a congratulatory letter and later wrote an episode inspired by the exchange. Speaking about the incident later on, Griffin told a local newspaper, "I felt like it was part of history-making television.”

New York Yankees star players Derek Jeter and Bernie Williams popped up on the show in 1996. In one of their scenes, a clueless George, who works for the organization on the series, attempts to give tips to the two pros on how to hit the ball.