I've recently learned that the game's developers originally had a line of dialogue for Dormin where he first describes Valus.  The text is in the program code but wasn't present within the game itself.  This same text goes like this:

"Thy first foe is...

A giant that walks along the valley...

The servan shall rise from behind...

and make the earth quiver."

I found it from this video posted by the well-known Nomad Colossus:

Shadow of the Colossus - Odds & Ends (part 2)

Shadow of the Colossus - Odds & Ends (part 2)

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