William Daniels reveals what fans don't know about 'Boy Meets World' and more

Daniels' memoir, "There I Go Again," is on sale now.

ABC News caught up with the 89-year-old together with actress Bonnie Bartlett, his wife of 66 years, on the heels of the publication of his new memoir, "There I Go Again: How I Came to Be Mr. Feeny, John Adams, Dr. Craig, KITT, and Many Others."

Here's everything you never knew about William Daniels' most iconic roles.

Daniels was hesitant about being Mr. George Feeny

From 1993 to 2000, Daniels played the recurring role of a teacher and neighbor of the Matthews family, Mr. Feeny.

Daniels told ABC News that he wasn't too keen about the part at first until it was rewritten to his liking.

"I thought Mr. Feeny would be OK if they didn't write it as a foolish teacher," Daniels said. "I respect teaching, and they're underpaid, and I wanted to make sure -- the producer, Michael Jacobs, assured me -- that they wouldn't make fun of this character, that it was based on a teacher that he had in high school, that he respected a great deal. So I was reassured that way, and he kept his word.

"We didn't make him a foolish man ... well, sometimes," Daniels added, laughing.

Although he was hesitant to take on Feeny, Daniels admits that the character still lives on in the hearts of many fans.

"We were walking down in New York here, maybe 48th Street and a bus of kids came off the bus and they saw me, and they said, 'Feeny!' and I ran around the block," Williams said, with a laugh. "I was a total coward."

He was skeptical about voicing a talking car

For four years, Daniels was the voice of K.I.T.T., the artificially intelligent car from the 1980s adventure series, "Knight Rider."

Daniels was given the script before it was pitched by a producer, he said.

"I picked up the script [and said], 'This is a car? And it talks?'" Daniels recalled. "I read it and I left and that was that. About three weeks later, he said, 'I sold it, would you do it?'"

Daniels said that at the time he was appearing in "St. Elsewhere" at the same network as "Knight Rider," making it easier for him to say yes to the part. "So, I did it," he said.

"The Graduate" had some hurdles in casting

"Mike had let him go and then he brought the cast together and said, 'I want to apologize to you because this man is a great actor, but he's just wrong for the role that I saw and I made a mistake,'" Daniels said. "He told us that, the whole cast, so we knew what happened so we wouldn't be so nervous about getting fired.

"And he was right, because Gene went on to do wonderful things."

Daniels' memoir, "There I Go Again," is on sale now.

"Click here ," to watch the full ABC News Livestream with William Daniels and Bonnie Bartlett.