A post (way early on) mentioned the late Scottish tenor Kenneth McKellar, who was originally in forestry work before committing to classical voice training. An expert critic pronounced him the best singer of Handel's repertoire, and there are examples on YouTube (find Ombre ma Fui?) to convince. However, as far as I know, he never had much of an opera career other than recording material -- though I'm willing to be corrected,

But he also had a long career based on his sensitive interpretations of Scots song (Burns in particular, but also a repertoire that even veered towards the music hall, with some of his own self-penned comic songs). He had a series of television programmes over many years which promoted a real variety of musical styles, and he was pleasing in everything he attempted IMO.

The main point I want to make is that he had a truly musical voice with great technique which never got in the way of communication -- an instinctive sense of the importance of the words, a very natural and clear vowel sound, and a real warmth.