The only thing to fear is loss of ambition. But if you’ve got plenty of that, then you have nothing to fear at all’ – neil degrasse tyson neil degrasse tyson is arguably the most influential, acclaimed scientist on the planet. As director of the hayden planetarium, and host of cosmos and startalk, he has dedicated his life to exploring and explaining the mysteries of the universe. Every year, he receives thousands of letters – from students to prisoners, scientists to priests.