"Jupiter, the Bringer of Jollity" is just as influential, with its multifaceted internal movements providing inspiration for a diverse set of other pieces. Holst himself adapted part of the theme to the hymn "I Vow to Thee, My Country", and it has been heard in pure or adapted form in Bill Conti's music for The Right Stuff, the 2003 World Cup music, and even an advertisement for Reeses' Peanut Butter Cups!
For me, however, "Jupiter" is perhaps the core theme of my entire main multiverse, and specifically inspired and continues to inspire the imagery and characters of any space-setting adventures, and in particular also is the theme that represents Terian the Infinite, the Mortal God. I built my earliest writing around the feelings expressed in that piece.
While the name of the piece says "Jollity", the sound of "Jupiter" says, to me, "Heroism". It is perhaps THE most uplifting piece of instrumental music, with its only true competition being the most-played movement of Beethoven's Ninth Symphony.
The version of Jupiter linked above is the one that first inspired me -- by Leopold Stokowsky and the Los Angeles Philharmonic Orchestra. If you haven't listened to it before, give it a try. If you have... you probably already know what I was trying to say here.