Rod Serling never planned to narrate The Twilight Zone
Serling wasn't meant to be the face of the show.
There are writers, and there are TV stars. Rarely do the two ever intersect. Sure, folks like Alan Alda and Tina Fey exist in the center of that Venn diagram. But, for every example for which this is true, hundreds of writers do not act and hundreds of actors do not write. They're incredibly different jobs! One can be done mostly in solitude, while the other requires a set or filled with other professionals.
Occasionally, though, there's a writer so important to a series that their profile is raised to include on-air performances. That was the case for Rod Serling, who created The Twilight Zone and wrote many of its teleplays. Serling was the singular creative engine of the series. Even when he didn't write an episode, each script had to meet his standards and suit his creative voice. Rod Serling was the most important person involved in producing The Twilight Zone, so he was thrust, somewhat reluctantly, into the spotlight.
In a 1983 interview with The Roanoke Times, his widow set the record straight regarding Serling on screen.
"He was a writer through and through," Mrs. Serling said. He didn't intend to narrate it. [...] There were plans to get Orson Welles, but Orson was in London and he was a little expensive."
So Serling became not only the show's creative center but also its identity. Rod Serling was the face of The Twilight Zone, and his presence alerted viewers that things were about to get weird.
"He had a point of view," said Mrs. Serling. "He wanted to say something about the social condition. He literally escaped into The Twilight Zone."