Andrej is an extremely effective communicator and educator. But I don't agree that he is one of the most significant AI pioneers in history. His research contributions are significant but not exceptional compared to other folks around him at the time. He got famous for free online courses, not his research. His work at Tesla was not exactly a rousing success.
Today I see him as a major influence in how people, especially tech people, think about AI tools. That's valuable. But I don't really think it makes him a pioneer.
You can debate the meaning of the word pioneer but think of it this way: OpenAI created this new AI boom, and Andrej is a co-founder of the company that did that.
Would you say that Musk is one of the most significant AI pioneers in history? I don't personally believe that founding the organization is more meaningful than doing the actual work.