Slartibartfast is not named for the majority of the episode he first appears in. Word Of God explained that it was a joke at the expense of the woman who had to type the scripts - that she'd typed this name a dozen times and he simply said 'My name is not important'.
The seventh episode was originally broadcast on 24 December 1978. Consideration was given, partly due to the date and partly due to the fact that all the plot threads had been tied off at the end of episode six, to making it a stand-alone Christmas special in which Marvin would have been both figuratively and literally the star (of Bethlehem), and by participating in a nativity scene would be cured of his depression. In the end they made it a normal episode, devoted to untying enough plot threads for the series to continue.
Hey, It's That Voice!: In the recent radio adaptations we have Christian Slater as Wonko the Sane, Jackie Mason as The East River Creature and Stephen Fry (again) as Murray Bost Henson. The gent who would later become familiar as the voice of Danger Mouse, David Jason, was the Golgafrincham "B" Ark Captain in the primary phase series.
And Jim Broadbent played one of the complaining philosophers and one of the gun-happy cops on Magrathea.
Real Song Theme Tune: The theme for the radio show was a snatch of "Journey Of The Sorceror" by the Eagles from their 1975 album "One Of These Nights." It would be re-orchestrated for the TV series.
Darth Vader is Hotblack Desiato's bodyguard, and is responsible for his body. (David Prowse wore the Vader suit in Star Wars, but didn't do the voice.)
Prop Recycling: The background characters in the restaurant at the end of the universe are equipped almost entirely with costumes recycled from earlier episodes, and in particular from the various Guide entries, thus helping justify the expense of items which otherwise would have appeared on screen for only a few seconds each.