In case you have no idea who Carl Sagan is... well, you should, basically. Carl Sagan is one of those men who brought science to the people, making numerous fields such as astronomy, astrophysics, exobiology, and many, many more accessible for the masses. He published more than six hundred research papers and popular science works, and reached the minds and hearts of millions. He also wrote the novel 'Contact', after which a movie was made (despite the fact that it doesn't quite follow the book).
He also made a wonderful series of documentaries, which I highly recommend for absolutely everybody. Entitled 'Cosmos: a personal voyage', the series lucidly and clearly explains topics such as Einstein's theory of relativity, Darwin's evolutionary theory, pollution, how galaxies are formed, etc. The 13 hours of documentaries should make their way onto television all the time if you ask me, but until then, you can grab them from here. Sadly, not all of them can be embedded here, so I will only put the link for these ones.
Carl Sagans Cosmos - Episode 1 - The Shores Of The Cosmic Ocean:
Carl Sagans Cosmos - Episode 2 - One Voice In The Cosmic Fugue
Carl Sagans Cosmos - Episode 3 - The Harmony Of The Worlds
Carl Sagans Cosmos - Episode 4 - Heaven & Hell
Carl Sagans Cosmos - Episode 5 - Blues for a Red Planet
Carl Sagans Cosmos - Episode 8 - Journeys in Space & Time
Carl Sagans Cosmos - Episode 9 - The Lives of the Stars
Carl Sagans Cosmos - Episode 10 - The Edge of Forever
Carl Sagans Cosmos - Episode 11 -The Persistence of Memory
Carl Sagans Cosmos - Episode 12 - Encyclopædia Galactica
Carl Sagans Cosmos - Episode 13 - Who Speaks for Earth?