He was a control freak. Naturally, I would assume that he had the same controlling approach to Avatar and Titanic, both largely successful box office hits.
Everyone loved working with James Cameron because he knew how to challenge his team. He knew how to set out and paint a grand vision -- and he definitely knew how to make it a reality. That said, when it comes to his films, it is his way or the highway. I can understand this since he wrote the scripts, pitched to studios, and got the funding necessary to make it happen. In one particular case, Arnold Schwarzenegger absolutely hated the line "I'll be back" -- it sounded too girly for a killer robot. James Cameron wrote the script as, "I'll be back" but Arnold Schwarzenegger wanted to remove the contraction by saying, "I will be back" -- it seemed more in line with what a robot would say. In the heated situation, James Cameron ended the argument by saying, "Look, I don't tell you how to act and you don't tell me how to write. Just say the damn line."
Terminator went on to be a box office hit -- one of the most legendary films ever made in history and the line "I'll be back" became the most popular phrase in movie history. The thing about James Cameron was his intuition. He knew deep down what would be amazing for the people to see and what people want to see on the big screen.
Relating to startup founders, I think that a lot of highly successful startup founders have the same approach to achieving big goals including Jeff Bezos (Amazon), Bill Gates (Microsoft), Steve Jobs (Apple), and Thomas Watson (IBM). They had the ability to see into the future, paint a grand vision, share that vision with the team and challenge the team to make it a reality.