Nope.

Maybe Eomer?

Or some sort of Turgon? (the Steward) That's quite random... but it's sort of hard to see what is the connection you're looking for. Tricky, Miggy! :)

*coughcough* Miggy?

Sorry about that, no still no correct answers.
I'll use a Latin proverb to give you a big hint - in vino veritas!

Ah.Truth.

Gandalf,then

No, it's not Gandalf.
Also, I would appreciate explanations, that way I can provide hints with what is wrong about the guesses.

I've been wondering for quite a while whether it shouldn't read "________ to Théoden" instead of other way round like you put it, TM. Looking at the relationship between Pippin and Denethor, what have we got?
1.) Pippin told Denethor how his son died,
2.) swore fealty to him,
3.) served him as his squire and, I believe, cup-bearer (the in-vino-veritas hint could refer to this),
4.) disobeyed his orders to save Faramir's life.
I can think of several people who performed one or more of these services for Théoden, but no instance of Théoden himself doing anything of the like.:(

No, no, it's correct this way.

Still no takers?
One of Pitch's points is very close to the answer.

For some reason I think it has to something with either Saruman or Wormtongue

No, but close.
The answer does come from Rohan, and keep in mind the vino hint, should be easy then.

Merry Brandybuck became a squire for king Theoden...is it Merry?

No, as I said the answer does indeed come from Rohan, as in born and raised there.

The only person that was born and raised in Rohan who had anything to do with wine is Eowyn. She passed the cup of wine around during Theoden's first dinner/lunch with Gandalf, Aragorn, Gimli, and Legolas.
But I honestly don't know how that can fit with Pippin and Denethor. Except for maybe Theoden and Pippin are both trying to convince Eowyn and Denethor not to lose hope and faith...

Might???

Revival Time!
 

And I will use both one of my favorite characters and an interesting find I've found in this one.



Maeglin is to Glirhuin as Saeros is to ____