There are some professors you never forget. They burrow into your memory through their style as well as their substance and, with time, it is usually the style that remains.
Some who stay with me:
The constitutional law professor who chain-smoked throughout his lectures and who could quote obscure dissents and facts. He never went near any notes, but would lean against the blackboard - that term dates me - and would occasionally mistake the chalk for the cigarette. His lectures were fascinating.
The history professor who would spice his Soviet History classes with anecdotes about Lenin and Stalin, jump up on his desk top to make dramatic points, and sometimes conclude class by singing Russian folk songs.
The law professor who, unlike most of his colleagues, treated the students with respect and would respond to every question by following a pattern. His approach could be easily mocked as:
Student: "Why did the chicken cross the road?"
Professor R: "That's a very good question from a very good man. Now I know you didn't mean to ask that question. What you meant to ask was, 'How, given the history of the common law, can the reasoning of no fault divorce be justified?' And the answer is: 'To get to the other side.'"
One of my professors, whose specialty was the American Civil War, was famous for dissolving into tears whenever he read Lincoln's second inaugural address. He loved his subject and he transmitted that love to his students.
Four very different professors and yet they had a common and very appealing trait: a passion for their subject.