Short answers, pulled from the story.
Carl Sagan was best known for co-writing and narrating the 1980 PBS documentary series Cosmos: A Personal Voyage, which was seen by at least 500 million people in 60 countries and won two Emmy Awards and a Peabody Award. He was also a planetary scientist who contributed to the Mariner, Viking, and Voyager space programs, and won the 1978 Pulitzer Prize for General Nonfiction for The Dragons of Eden.
Harvard denied Sagan tenure in 1968 partly because his interests spanned too many disciplines at a time when academia rewarded narrow specialization, and partly due to a letter from Nobel laureate Harold Urey strongly recommending against it. Some colleagues also felt his public scientific advocacy amounted to self-promotion rather than original research.
The Voyager Golden Record was a disc sent with the Voyager space probes in 1977 containing samples of Earth's sights and sounds, designed as a universal message for any intelligence that might find it. Sagan contributed to its creation; among its contents are musical works by Bach, Beethoven, and Chuck Berry.
The Sagan standard is the maxim that extraordinary claims require extraordinary evidence. Sagan made it famous, but it was based on a nearly identical statement by Marcello Truzzi, and the underlying idea traces back to Pierre-Simon Laplace's principle that the weight of evidence should be proportioned to the strangeness of the facts.
In 1983, Sagan was one of five authors, known collectively as the TTAPS group, who published the scientific paper that introduced the term "nuclear winter." The term itself was coined by his colleague Richard P. Turco. Sagan went on to co-author books on the subject and was arrested twice at the Nevada Test Site during anti-nuclear protests in 1986.
Sagan never used the phrase "billions and billions" in that exact form; he used "billions upon billions." The catchphrase became associated with him after Johnny Carson parodied his distinctive way of emphasizing the letter b in "billions" on the Tonight Show. Sagan embraced the joke and titled his final book Billions and Billions.