The Restaurant at the End of the Universe is Douglas Adams' Favorite Hitchhiker Book.
Life, the Universe and Everything was originally planned on being a Dr Who story, called 'Dr Who and the Krikkitmen', but the Dr Who people thought it was "too silly"
Douglas Adams technically did 3 Dr. Who stories,'Pirate Planet','City of Death',and 'Shada', But 'Shada' never hit the airwaves, just the home video medium.(Actually, 4, if you count Dr Who and the Krittitmen, which evolved into Life, the Universe and Everything)
When doing the first Hitchhiker Radio Series, Douglas Adams did not think there would be a second series. Therefore, since he did not leave the ending open, it was hard to open it up again when a second series was wanted. So at the end of the second series, Douglas left it open for a third. There never was a third series.
Douglas had planned on only having two hitchhiker books, even though he ended up with 5, possibly more.
According the the much told story, Douglas Adams first came up with the idea for Hitchhikers when he was lying drunk in a feild in Insbruck, Austria with a copy of 'The Hitchhikers Guide to Europe' and said to himself that someone should write a 'Hitchhikers Guide to the Galaxy'. Little did he know it would be him.
Douglas once did a guest spot on Richard Dawkin's television show.
Douglas Adams and John Lloyd once wrote episodes for the British children's television show, Dr. Snuggles.
Marvin, Everybody's Favorite Robot, released a series of single albums(Voiced by Stephen Moore)in 1981. 'Marvin/'Metal Man',and 'Reasons To Be Miserable'/'Marvin I Love You'. The First One even reached number 53 on the charts, making Marvin the only robot ever listed in the 'Guiness Book of British Hit Singles'. The second one didn't do so well, and because of this an unheard third Marvin single, a christmas song, never made it as far as the final mix.
The same actor who played Hotblack Desiato's bodyguard in the Hitchhiker TV series also played the body of Darth Vader in 'Star Wars'