Final answer:
Carl Sagan, the American astronomer, authored 'Cosmos' and was known for his contributions to popularizing astronomy and his study of extraterrestrial life. His books and television series have had a lasting impact on both the scientific community and the general public.
Step-by-step explanation:
The American astronomer who wrote Cosmos and studied extraterrestrial life is Carl Sagan. Known for his work in popularizing astronomy, he authored multiple books including Cosmos, The Cosmic Connection, Pale Blue Dot, and Contact which was later adapted into a film. His writings not only delve into the wonders of the universe but also confront pseudo-science and irrationality.
Carl Sagan became a household name in the late 20th century and made significant contributions towards educating the public about the solar system and the greater cosmos. His works remain fundamental for both astronomers and enthusiasts alike, fostering an understanding of the vastness of the universe and our place within it.
Additionally, Sagan's television series Cosmos: A Personal Voyage and the updated series Cosmos: A Spacetime Odyssey, hosted by Neil DeGrasse Tyson, have continued his legacy of bringing astronomy to the masses. Sagan's enduring impact on the field of astronomy and his efforts to raise public awareness about the importance of space exploration are still felt today.