Sometimes a character is so associated with their name (first name, family name, whichever) that no other character may ever again. Truly, how many heroes can live up to Roarke? Can any other Jamie carry the name as well? (Note, I’m not a Gabaldon fan, but I get that other readers think he’s all that and a bag of chips.)
I tried reading what seemed like a sweet historical, but was unable to finish because the hero’s name was Severus. And in my head, Severus = Severus Snape. Now, Severus Snape is a hero in J.K. Rowling’s series, however maligned, tortured and unhappy he may have been, and despite his poor choices as a young man. My problem isn’t that I see Alan Rickman in the romance novel hero’s place — that would be perfectly okay, although not really appropriate casting for this book. The problem is entirely in my head. The name Severus brings all the Snape baggage, which is inappropriate for this romance. Heroic he may have been, but damaged to such an extent that I could never believe in a HEA for him.** Which is making the mixing of the two characters in my head problematic for this book.
I have the same problem with a newish m/m contemporary — one of the MC’s is named Sirus. I know, an alternate spelling of the name Cyrus. But all I see on the page is Sirius. Sirius Black. This isn’t necessarily a bad thing or completely incongruent — let me just say that viewed through my slash goggles, Gary Oldman played Sirius as rather campy and jaded in the HP5 movie, especially when David Thewlis (Remus) was on screen at the same time. But that’s really not the image that the author is going for with his/her Sirus, I’m sure.
*FWIW, despite all the Snape fanfic with alternate endings and HEAs, if I wrote FF I’m not sure if I would keep him alive, although I would certainly give him a less ignominious death — his ultimate end was rather a let down given his sacrifices and importance in the series.