Like I've theorized way back in February:
The Elder Toad Sage was probably Rikudou Sennin's contract summon, since only Rikudou and him have been shown with the gift of divination/prophecy, not to mention the Elder Toad is stated to be thousands of years old, which probably means he existed during Rikudou's Era.
Now take a look at this:
[Credits to AbsoluteAnime for the Photo]
More than once, the name "Arashi Uzumaki" has been shown to be written in the Toad's Summon Contract.
It is quite strange since in later chapters, Minato's name appears in Arashi's place:
Another oddity is that Naruto was not baffled as to why someone with his surname appears next to his.
This could either be clue or a retcon. It could be that Kishimoto decided to save Arashi Uzumaki's name later on for another character: Rikudou Sennin
This could be Rikudou Sennin's Real Name: "Arashi Uzumaki"
It would be a perfect name for Rikudou Sennin:
Arashi 嵐 means "Storm"
Uzumaki うずまき means "Whirlpool"
So if we combine his name it would be:
Arashi Uzumaki: 嵐うずまき which literally translates into "Storm Spiral/Whirlpool"
We know the Sage's title is 六道仙人 or Rikudō Sennin or Sage of the Six Paths, but what if his title was also a clue to his name?
Rikudō roughly translates to Six Paths/Six Immortal Paths, Riku could mean Six and it could also mean "Land/Continent" or "Shore". Uzumaki 渦中 means Vortex/Whirlpool, now if S06P was an Uzumaki and his name was Riku, he would be Riku Uzumaki which would mean "Land of Whirlpools" If he was a Sennin or "Sage" then he would be called Sennin Riku Uzumaki セナりくうずまき or "Sage of the Land of Whirlpools"
So its either Arashi Uzumaki or Riku Uzumaki