Let Me See...In junior high school (secundaria) it was Mrs. Bertha Brassea, our Biology teacher. She had a passion for the subject, and transmitted it to us. If I were to teach again, I would just hope to have a fraction of her ability.
In senior high school (preparatoria), it was Mr. Adalberto Calderón, the Mathematics teacher. He really wasn't a good teacher, as he was the typical dictator. But he demanded a lot, and certainly made a difference.
In college it was Mrs. Anna Suchanek. She gave me Advanced calculus. She taught me to write mathematical proofs.