Happy to see John Whitlock III mentioned!
I was thinking of who my most influential instructors have been, and the first that comes to mind is III's father, John "Corky" Whitlock. I worked with him as a teen-ager in the St. Paul Scouts, and later with (Minnesota) Brass Inc.
I think what I've learned most from Cork is to put some style in my playing -- not that I've achieved his level. I can recall him playing right through a "wrong" note and making it sound so cool and so right! And he really knew (knows) how to ghost a note. And he really taught us how to blow!
He passed a lot of his gifts along to his successor, Rick Rueckert.
I'm happy when I can hear some of Corky's "voice" in my playing when I play something well, especially if it's an improv solo.
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On the other side of the coin, Robb Muller has been most influential to me in recent years. I say the other side of the coin, because at this point in MBI's development, Robb's influence wasn't about loud, but all about quality of sound, intonation, and blend, and making a horn line even more powerful than one that's merely loud. Even though MBI produced great horn lines over the years, Robb brought a new level of quality and serious musicianship to the line. "Being good is fun." (Love ya, man!)
The most amazing thing about Robb as a horn line teacher, is that he's a percussionist, and has taught top-level drum lines as well.