Carl Sagan guided the maiden voyage of Cosmos a generation ago. He was the most successful science communicator of the 20th century, but he was first and foremost a scientist. Carl contributed enormously to our knowledge of the planets. He correctly predicted the existence of methane lakes on Saturn’s giant moon Titan. He showed that the atmosphere of the early Earth must have contained powerful greenhouse gasses. He was the first to understand that seasonal changes on Mars were due to wind-blown dust. Carl was a pioneer in the search for extraterrestrial life and intelligence. He played a leading role in every major spacecraft mission to explore the solar system during the first 40 years of the space age.