1. Tom Baker
The man himself. Of course he is the number one reason why his era is so iconic. In many ways, Tom Baker's Doctor has been extremely influential on many subsequent Doctors. And yet at the same time, there is no Doctor quite like Tom Baker.
A key reason for this is Tom Baker himself. Watching him in interviews, the man clearly brought a lot of himself to the role, as there's no one else in the world quite like Tom Baker. I remember during one interview he gave in the 1999 documentary Adventures in Space and Time, he described that the best way of playing someone strange and alien "was just to play Tom Baker".
It was a method that worked brilliantly. It wasn't just that no one had seen a Doctor like Tom Baker's before. It was that no one had seen a performance like his. From the very beginning, he gave his Doctor the sense of someone who was truly alien, who wasn't of this planet. Whether he was displaying wisdom, making a clever observation, or even just being funny, there was always an incredibly alien quality about Tom Baker's Doctor.
And his performance was consistently brilliant. One of the most iconic moments in Doctor Who's long history is the Doctor's dilemma of whether he has the right to commit genocide on the Daleks. It's an amazing moment to watch that Baker completely commits to. Even more amazing is that it's from his first season.
We've had so many great Doctors, both before and since Tom Baker. But, five decades since we saw him wake up in "Robot", he's still one of the most popular Doctors. And thanks to all of these reasons, that will continue to prove true for decades to come.