Marisa Tomei Almost Played 'The Big Bang Theory' 's Penny: 'What a Different World That Would Have Been'

In an alternate universe, Marisa Tomei won the role of Penny on The Big Bang Theory instead of Kaley Cuoco.

An excerpt of Jessica Radloff's soon-to-be-released oral history of the CBS sitcom shared with The Hollywood Reporter reveals that the My Cousin Vinny star was one of several actresses under consideration for the beloved character.

According to The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series, the show's creators initially had a very different Penny in mind — for starters, her name wasn't even Penny.

The character was originally called Katie, and Cuoco was so incompatible with the role that she almost missed out on it completely.

"[Cuoco is] so sunny and bubbly, and [the network] just loved her, but she just didn't bring the dark qualities," said casting director Ken Miller. "She just wasn't the essence of Penny in that first incarnation."

Though "bummed" after initially losing out on a role she "loved," Cuoco, now 36, made peace with the situation, telling Radloff, "I kind of have a way of moving on because you have to."

At that point, Tomei, now 57, entered the picture and read for the role with Jim Parsons, who had already been cast as Sheldon.

"Oh my gosh what a different world that would have been," said Parsons, 49.

Big Bang Theory co-creator Bill Prady says that both Tara Reid and Elizabeth Berkley also pursued the role of Katie/Penny. She's All That star Jodi Lyn O'Keefe was ultimately cast as Katie and went as far as starring in the original pilot alongside Parsons and Johnny Galecki.

Valko said O'Keefe was "so good" as Katie, but things just hadn't fallen into place yet.

"It was just a totally different character," the casting director said. "[O'Keefe] brought a darkness, which just didn't work, so she was replaced [by Canadian actress Amanda Walsh] after the table read."

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Though THR's excerpt doesn't include what exactly went down to lead to Cuoco landing her signature role — and an off-screen romance with Galecki during Big Bang's run — it's sure to be included in Radloff's The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series, which will be available everywhere books are sold on Tuesday.