Halfway through the 20-year run of the The Lone Ranger radio serial, Earle Graser, who played the Ranger, died in a car crash, mandating a quick replacement. The producers covered up the voice change by having the Lone Ranger get shot in the neck by an arrow, requiring Tonto to speak on his behalf for several weeks, until Brace Beemer was chosen as the new Ranger.
Howard Duff was replaced as radio's Sam Spade (on The Adventures of Sam Spade) by Steve Dunne, who sounded nothing like Duff.
On the other hand, when Harold Peary left The Great Gildersleeve, his replacement, Willard Waterman, sounded so much like Peary that few listeners could tell the difference.
In the original two phases of The Hitchhikers Guide To The Galaxy radio series, the voice of the Guide was done by Peter Jones. In the newer three phases it was William Franklyn. Lampshaded as an 'upgrading' of the guide with an extremely well-edited merging of the two voices at the beginning of the third phase. A few other voices were changed as well, such as Eddie, Slartibartfst, and Prostetnic Vogon Jeltz. However, given the long span of time between the recording of the second and third phases, and the fact that most of the not-returning actors had passed away, this is understandable and for the most part the series did an excellent job of maintaining the cast. Even Jonathan Pryce (a much morerecognizableactor since he was first heard in Hitchhiker's) returned as Zarniwoop.
Tom Conway replaced Basil Rathbone on the old Sherlock Holmes radio series.
On The Shadow, Lamont Cranston and Margo Lane were each portrayed by a succession of voice actors.
The Whistler was portrayed by several different actors during the course of its run.
Yours Truly, Johnny Dollar had the distinction of being the last radio show of America's Golden Age of Radio, ending in 1961. The most popular of Johnny's six distinct voices, Mandel Kramer, also happened to be the last.
Adric is voiced by Andrew Sachs instead of Matthew Waterhouse in the audio "The Boy That Time Forgot" because Waterhouse, who last played Adric in the Doctor Who serial Earthshock in 1982, declined to participate. The change is still acceptable because Adric is no longer a kid but several hundred years old.
In "The Light at the End", the First and Second Doctors are played by William Russell (who played the First Doctor's companion Ian Chesterton) and Frazer Hines (who played the Second Doctor's companion Jamie) respectively. The Third Doctor is played by an impressionist.
All of the Companion Chronicles audios are prose stories that have the companion actor playing their Doctor, as well as themselves. Some of them use a Framing Device to explain that the companion is telling the story, and others don't and do it as a stylistic quirk - while some other audios use it for Metafiction (like "The Time Museum"). The quality of the impressions varies, but total accuracy in voice tone isn't the goal (especially as most Doctors end up being played by women more often than not) - most of them do a bang-on job of getting their Doctor's mannerisms down.
In "The Kingmaker", the Fifth Doctor is made to finish a book he was contractually obligated to write. He listens back to some outdated voice notes made when he'd last tried working on it, which turns out to have been a whole other regeneration ago. The Fourth Doctor in this scene is played by Jon Culshaw from Dead Ringers, who is known for his uncanny impression of Tom Baker's voice.
In Big Finish's "The Early Adventures" series, companions played by deceased actors were recast for the first time. Barbara Wright was recast with Jemma Powell, the actress who played Barbara's original actress Jacqueline Hill in An Adventure in Space and Time. Ben Jackson was recast with Elliot Chapman.
When Benedict Cumberbatch came down with a nasty case of laryngitis, Tom Goodman-Hill stepped in as Captain Martin Crieff for Cabin Pressure's third-series episode "Newcastle". Although he didn't sound exactly like Cumberbatch, he did do an excellent job of mimicking the latter's speech patterns.
On at least one occasion Dick Emery played the part of Neddie Seagoon in place of "Harry Secombe" in the "Radio: The Goon Show". Lampshaded by the fact that he is referred to as Emery Type Seagoon.
Star Wars Radio Dramas: With a few exceptions, such as Anthony Daniels as C-3P0, pretty much every role was recast during the transition from film to radio. However, between the three separate adaptations, there were also some cast changes:
Luke Skywalker:A New Hope and The Empire Strikes Back featured Mark Hamill reprising his film role as Luke. However, he declined to return for Return of the Jedi, and Joshua Fardon was cast in his place.
Lando Calrissian:The Empire Strikes Back featured Billy Dee Williams reprising his film role, but Lando was played in Return of the Jedi by Arye Gross.
Boba Fett: In The Empire Strikes Back he was played by Alan Rosenburg, but Ed Begley, Jr. assumed the part in Return of the Jedi.
Wedge Antilles: This character was heard in all three series, and was played by three different actors.
The Emperor: Unlike in the films, however (at least, before the Special Editions) the Emperor was played by the same performer (Paul Hecht) in both The Empire Strikes Back and Return of the Jedi.