Taking one of Professor John Fraser Hart's geography classes at the University of Minnesota is like taking a step back in time.

The World War II veteran is known for donning a bow tie and using a carousel slide projector to show off his collection of tens of thousands of Kodachrome slides of landscapes across the country, all of which he's taken himself.

"In some ways he feels like he is a relic of an earlier time but he doesn't apologize for it at all," said retired University of Minnesota professor John Adams, who worked with Hart for nearly 40 years.

While Hart's style may not appeal to everyone, many students praise him in online reviews, noting his "wacky sense of humor" and his "all-around charming and entertaining" personality.

Related: Meet the country's roving retirees

In more than 50 years of teaching, Hart has published 15 books and taught more than 50,000 students.

While he could have afforded to retire long ago, Hart said he simply loves his job too much.

"I've learned a lot and I have a chance to share with students," he said. "Each year, I think I keep getting a little bit better at what I'm doing."