Michael J. Fox thanked Crispin Glover for being a "brilliant actor" to work with on Back to the Future 40 years after the film's release

It comes as Michael gained a deeper appreciation for Crispin after he rewatched Back to the Future to write his memoir, Future Boy - Michael's account of making the movie.

Michael wrote in the book: "In the process of preparing for this book, I wrote Crispin a letter.

"'Your performance is richer and deeper every time I see it. In fact, I skip over my bits to watch yours. Granted, we didn't talk much during production, so I never had the chance to say that you are a brilliant actor, and I was thrilled to work with you.'"

In 1984, Michael and Crispin starred opposite each other on a season two episode of the sitcom Family Ties, titled Birthday Boy.

Crispin played Doug, a pal of Alex P. Keaton (Michael), and his delivery of several lines bagged him "the biggest laughs" of that episode.

Michael recalled in Future Boy: "The interesting thing about Crispin as an actor is that he had no awareness of the audience. He wasn't trying to milk the laughs.

"He was just naturally funny, and he crushed it on every take. I feel the same about his work in Back to the Future."

When it came to Back to the Future - which starred seasoned actors, including Christopher Lloyd (Dr. Emmett "Doc" Brown), but most of the cast were rising stars - Michael could not prepare to work with Crispin.

Michael explained in his memoir: "I knew Crispin Glover prior to Back to the Future. I wouldn't, however, say I was prepared to act with him -¬ there's no way to prepare for Crispin.

"With Chris Lloyd, I had an inkling of what he was up to. Neither he nor Crispin ever did the same thing the same way twice.

"But as a trained theatre actor, Chris was much more locked into the script, so there was that constant to depend on.

"I never knew what Crispin was going to say or do. I'm not sure he knew, either."

Crispin loved having a say on how his character should be written, which "often caused tension with [screenwriter] Bob Gale and [director] Bob Zemeckis".

Michael penned in Future Boy: "Nobody puts Crispin in a box. As George McFly, Crispin had his own ideas as to how and where his character should move."

Crispin did not return for the sequels Back to the Future II and Back to the Future III due to reported creative differences and a salary dispute.

Instead, Jeffrey Weissman, 67, took on his role of George McFly.