In his long career, Stephen Hawking set the agenda for other physicists, including CBS News science and futurist contributor Michio Kaku. Kaku, a physics professor at City University of New York, calls Hawking the "rock star of science."

"We look up at the night sky, we see all these stars, and we wonder what does it all mean? Where did it come from, the universe, and where is it going? And here was the man, not since [Albert] Einstein, who could communicate to the public about the meaning in the universe itself. Cosmic questions that we all think about at night," Kaku said Wednesday on "CBS This Morning."

Hawking died early Wednesday at the age of 76. His research answered many mysteries of time, space and black holes. He became a best-selling author with his 1988 book, "A Brief History of Time," and went on to become a pop culture celebrity. He did this against all odds, living with Lou Gehrig's disease for more than 50 years.

"All of my life I have sought to understand the universe and find answers to these questions. I have been very lucky that my disability has not been a serious handicap. Indeed, it has probably given me more time than most people to pursue the quest for knowledge," Hawking said at TED2008.

He also helped resolve contradictions between Einstein's General Theory of Relativity and the Theory of Quantum Mechanics.

"We learned that Einstein's theory is incomplete. In fact, Einstein himself was looking for a theory of everything that would unite quantum mechanics, atomic physics, with black holes. And so what Hawking did was he showed that black holes are not really black, overturning decades of thinking," Kaku said. "Black holes are gray. They emit what is called Hawking radiation. And that's what happens when you apply quantum mechanics to black holes. So he set the agenda. He was the first person to get meaningful results when you combine these two great theories."

Kaku, who has met Hawking and spoke at a conference the late scientist organized, said he was struck by Hawking's determination.

"He was determined to be at the forefront of physics even when he was paralyzed, something that would have crushed – crushed – an ordinary individual was a challenge for him. A challenge for him to overcome. And also he saw himself as sort of like a herald, warning us about the dangers of global warning, saying that we should explore outer space," Kaku said.

Hawking also had a "tremendous sense of humor."

"Even with his tremendous adversity, he would crack jokes at conferences and break up the entire conference. Because he wanted to interact with people. He loved to interact with people. And that's why I think he wrote his best selling books. Because you wanted to educate people, warn humanity about potential dangers, but also pave the way for a bright new era," Kaku said.