A Matter of Convention

Igor: Dr. Frankenstein…
Dr. Frederick Frankenstein: "Fronkensteen.“
Igor: You’re putting me on.
Dr. Frederick Frankenstein: No, it’s pronounced "Fronkensteen.”
Igor: Do you also say “Froaderick”?
Dr. Frederick Frankenstein: No…Frederick.“
Igor: Well, why isn’t it "Froaderick Fronkensteen”?
Dr. Frederick Frankenstein: It isn’t; it’s “Frederick Fronkensteen.”
Igor: I see.
Dr. Frederick Frankenstein: You must be Igor.
[He pronounces it ee-gor]
Igor: No, it’s pronounced “eye-gor.”
Dr. Frederick Frankenstein: But they told me it was “ee-gor.”
Igor: Well, they were wrong then, weren’t they?

-Mel Brooks and Gene Wilder in Young Frankenstein (1974)

[www.poemofquotes.com/funny-quotes/young-frankenstein-quotes.php]