TODAY is the day Emmett Lathrop "Doc" Brown, Ph.D. will arrive in the present from his "own time" of 1985.
It was fictionalised in the now-classic 1980s film Back to the Future.
To honour the day, Christopher Lloyd has delivered a message to us living in the present.
"Great Scott, if my calculations are correct it is now precisely October 21, 2015.
"The future has finally arrived.
"Yes, it is different than we all thought.
"But don't worry, it just means your future hasn't been written yet. Noone's has.
"Your future is whatever you make it. So make it a good one."
For fans, this is the day that has been 30 years in the making.
Cinemas across the world are showing one-off screenings of the films to celebrate October 21, 2015, the date shown on his DeLorean time machine's dash board.
Welcome to the future!