Renowned cosmologist Stephen Hawking at a press conference in April, 2016 | Timothy A. Clary/AFP via Getty Images Stephen Hawking bewildered by Donald Trump Hawking called Trump ‘a demagogue who seems to appeal to the lowest common denominator.’

For Stephen Hawking, the world-renowned expert in theoretical physics and cosmology, the success of Donald Trump’s presidential campaign is a mystery.

Hawking called Trump "a demagogue who seems to appeal to the lowest common denominator,” during an appearance on the United Kingdom’s ITV network.

In addition to his scientific work, Hawking, who has a slow-progressing form of ALS, is a vocal advocate for individuals with disabilities. Trump drew criticism late last year on the campaign trail when he appeared to mock a New York Times reporter with a disability at a rally in South Carolina. Trump later denied mocking the reporter and said he had never met him.

During the same television appearance, Hawking urged British voters to vote in favor of keeping the U.K. in the European Union. The Brexit vote is scheduled for June 23 and a vote to leave the EU would cost Britain in terms of its economy, national security and scientific research, Hawking said.

"Gone are the days we could stand on our own against the world,” he said. “We need to be part of a larger group of nations, both for our security and our trade."