Christopher Nolan has joked that casting Sir Michael Caine in his movies is a no-brainer, because he sets a good example.
The British actor has appeared in every one of Christopher's films since the first Batman instalment, Batman Begins, in 2005.
"He comes so prepared and he is just so good with such a minimal effort. I cast him in every film just as an example to everyone else," the filmmaker told The Hollywood Reporter.
"He's just a lovely guy to be around. He jokes that he's my lucky charm. It was a very good strategy on his part."
Christopher kept mum about his next film Interstellar, which stars Matthew McConaughey, Anne Hathaway, Jessica Chastain and Michael, and follows a team of space explorers who travel through wormholes. But he heaped praise on his leading man.
"Mud showed me a side of Matthew's capabilities that I never knew was there. It was a transformative performance. From when I first saw it, I had an inside track on how great he could be," he said.
As for Matthew's performance in Interstellar, he said: "I needed someone who is very much an everyman, someone the audience could experience the story with. He's just a phenomenal, charismatic presence in the movie. His performance is shaping up to be extraordinary."
Christopher teased that the movie is a real "blockbuster".
"I grew up in an era that was a golden age of the blockbuster, when something we might call a family film could have universal appeal. That's something I want to see again," he said. "In terms of the tone of the film, it looks at where we are as a people and has a universality about human experience."
Interstellar is scheduled for release in November.