Much like Peter Falk was Columbo, Darren McGavin is Kolchak, and no one can replace him. Some people are so identified as their character that no one could ever really work in the role. The remake of Night Stalker just proves that point.
Yes. Whether a character is just a bare bones outline for a series or an adaptation of a character from a novel the actor can make such a huge difference. Shatner took Roddenberry's character outline and breathed so much life into the Kirk we came to know. It's no different with McGavin and Carl Kolchak.
Can anyone really imagine someone else playing Archie Bunker or Hawkeye Pierce or any number of so well defined fictional characters? Could anyone else ever play Dirty Harry and not stand in Eastwood's shadow? We've been hearing rumblings of a Magnum, P.I.
remake for years and yet I can't really envision anyone other than Tom Selleck as Magnum.
McGavin did numerous roles before and since The Night Stalker,
including a series as Mike Hammer (late 1950s), but McGavin will always be the definitive Carl Kolchak.