Transcript for Celebrating the work, mind and humor of Stephen Hawking

??? Finally tonight here, he opened our eyes to the universe, and opened our minds to true human strength. It was the movie celebrating the groundbreaking work of one of the smartest minds in the world. Professor Stephen hawking. I'm a cosmologist. What's that? I study the marriage of space and time. Reporter: The Cambridge university physicist who studied the nature of gravity and the origin of the universe. So, this black hole at the gunning of time. Brilliant. Reporter: The movie following hawking's journey. His diagnosis. A.L.S., Lou Gehrig's disease, at just 21. His voice gone, but hawking was never silenced. Physicist, father, philosopher. Married twice, three children, and he outlived his prognosis by more than 50 years. Doctors believe it was, in part, because it was diagnosed as such a young age. The body more able to fight it. Just two years ago, we sat down with him, asking about the possibility of interstellar travel. In your mind, know what you know already, what do you expect to find, things that would help us on Earth or is this just an intellectual pursuit? The rapid progress of technology for space exploration has improved people's lives in the past. So, it would not be surprising if it brought benefits. Reporter: And his trademark humor. I want to ask you about "The simpsons." Stephen hawking! The world's smartest man! Reporter: How does it feel to be a pop culture icon? I won't feel like a true pop culture icon until I've been on the Kardashians. Reporter: Be careful what you wish for. We saw his smile. And Diane once asking him about his children. And his advice. Remember to look up at the stars and not down at your feet. Reporter: Dr. Hawking once said to his family, "It would not be much of a universe if it wasn't home to the people you love." Thank you, Stephen hawking. And thank you for watching here on a Wednesday night. I'm David Muir. I hope to see you right back here tomorrow. Until then, good night.

This transcript has been automatically generated and may not be 100% accurate.