Carl Sagan was an American astronomer, astrophysicist, cosmologist, author, and science communicator. He is best known for his work as a science popularizer and communicator, and he was also a highly regarded astronomer and astrophysicist. He is credited with popularizing the term 'COSMOLOGY' and is considered one of the most influential scientists of the 20th century. He wrote several books on the subject of COSMOLOGY, including Cosmos, which became a bestseller and was made into a television series. He was also a professor at Cornell University and a member of the National Academy of Sciences.