One of the most popular film series of Hollywood's Golden Age was the Dr. Kildare series from MGM. The first film based on the character came from Paramount and starred Joel McCrea as the young doctor.
Lew Ayres took over the role in a series of 9 B movies. B movies from MGM looked costlier than A movies from anybody else!
The movies had fairly tight continuity with the same actors returning over an dover and multiple plot lines per movie. The running plot was the new doctor's relationship with his mentor, the crusty, wheelchair bound Dr. Gillespie, played by the great Lionel Barrymore.
When Ayres left the series, Louis B Mayer's studio felt the soap/detective series was too profitable to lose so no less than SIX more pictures were made, highlighting the Gillespie character with a series of new assistants including hot star Van Johnson for several installments.
Ayres returned to the role, again opposite Barrymore, for a radio version in the 1950s.
Lionel Barrymore had long passed by the time TV took a look at Kildare but Ayres shot a pilot. Ultimately it was newcomer Richard Chamberlain who made the role his own on TV, with veteran Raymond Massey bring his gravitas to the role of Dr. Gillespie.