The other two teachers I wanted to mention are both very famous, so you'll find that much has been written about them by others.
John Ingle's boundless enthusiasm was a great inspiration to me, and I think a lot about what he taught now that I'm teaching musical theatre performance. He had a moment before excercise in which you'd read a letter (of your own creation) to lead you in to your song - a spelling out of "the moment before" that still strikes me as brilliant. When Ingle was my teacher, we all accepted that his early aspirations to be an actor himself had been thwarted. So, for all of us, it's been a gleeful surprise that, after retiring from the school, he's worked very steadily as an actor ever since, mostly on soap operas. His students included Nicholas Cage, Richard Dreyfuss, Albert Brooks, Larraine Newman, David Schwimmer and Rob Reiner. And that's just the tip of the iceberg.
Lehman Engel was not the jolly ol' soul Ingle was (are you getting this straight? I was talking about Ingle, now I'm talking about Engel) and was often irrascible or mean. Which is why I loved him. As tough as he could be, commented on our neophyte musical theatre creations, I knew that the real world was probably a whole lot tougher. This business of a pedagogy - that there's actually a "good way" to write a musical, and that it can be taught - didn't exist before Lehman. And, while he's much criticized, it's not as if somebody's stated a better theory. So, obviously, he was of paramount importance to my development.