Theoden is definitely Old English for "king," but it's also very similar-sounding to the name of the hero in a novel that Tolkien fell in love with as a boy. Not everything has to be based on one source of inspiration and one source only.
But clearly you are unwilling to listen to me or anything I say, so I don't know why I bothered posting this. In fact, I'm thoroughly sick of this entire thread now. Congratulations.