Question: "For a celebrated actor, I was surprised at how ordinary he was." The "celebrated actor" refers, of course, to "he" (not "I"). However it seems to me the grammatical construction is wrong. By substituting the preposition "for" with "as" to read "As a celebrated actor, I was surprised at how ordinary he was," is now grammatically correct but drastically changes the meaning. How can I say what I want to say in plain conversational English?

Answer: 
> 
> For a celebrated actor, I was surprised at how ordinary he was.
> 
> 
> 

This is a [perfectly acceptable use of *for* indicating a comparison](http://dictionary.cambridge.org/dictionary/british/for#1-6), and it's pretty clear that *he* is the actor (although in theory it could refer to the *I*, in practice the choice of *for* over *as* would leave no doubt in the mind of the audience). If you wanted to make it doubly clear, you could change the order:

> 
> I was surprised at how ordinary he was for a celebrated actor.
> 
> 
>
In *writing*, I don't have a huge problem with your original formulation. I can't see a way to rearrange things that makes it clearer without making it more awkward.

For *conversational* English though, its way too long-winded. If I was just talking to my buds, it would be more like, "I was shocked. He's just a regular guy, not some hoity-toity1 celebrity."

1 - Sprinkle expletives to taste.