Stephen Hawking dead at 76: Celebrities, public figures, scientists pay tribute

Hawking, whose life was chronicled in the 2014 film "The Theory of Everything," had battled amyotrophic lateral sclerosis – aka ALS or Lou Gehrig's disease – for more than five decades.

Scientists, public figures and celebrities, including astrophysicist Neil deGrasse Tyson and pop singer Katy Perry, flocked to social media to pay tribute to Hawking. Here's what they had to say: