The narrator for DOCTOR DeSOTO is IAN THOMPSON.
You can find his filmography here: http://uk.imdb.com/name/nm0860221/
For some reason, IMDb credits Ian Thompson with the narration of DOCTOR DeSOTO in his filmography but does not give him the appropriate credit in the actual title. (I don't understand why.)
This is Ian Jacob Thompson, although most credits just list him as Ian Thompson. Ian Thompson has been in many television shows, mini-series, made for television movies, as well as a number of feature films.
I agree that it is terrible that someone's work is not appropriately credited.