My high school English teacher. Because of our different system overseas and a small school, I had the same teacher from 7th-12th grade in all but one year (I think my 10th grade teacher was someone else). He was punctilious on grammar, supportive of expression in creative writing, but really lifted my love of reading onto a different scale with carefully chosen set works, and really got me understanding poetry. In a strange twist of circumstances, by the time D19 was near high school we were in a different city, but he was teaching at the high school she was going to be at and I was sooo hoping he would teach her too - how cool would that be? But then we emigrated to the US and he retired that same year too. He passed away from cancer a few years ago, and the outpouring on his Facebook page showed how widely loved he was over his decades of teaching.
Not sure if this counts but one of my second year economics lecturers brought a whole fresh approach to the subject and consolidated my love for the subject (which I was only doing initially because two years of economics were required for the degree I started). Partly thanks to him I changed my major to economics and never looked back.