According to Wikipedia, although Frank Oz still occasionally performs as Cookie Monster, David Rudman has been performing Cookie Monster on Sesame Street since 2001. So it was probably him on Colbert.
“Purity!”
Oh, god, I’m crying. That was excellent.
Thanks for posting that. 
The one night this week I DON’T watch Colbert…
Somebody please tell me they too were getting turned on when Martha was caressing Cookie Monster.
Then she says, “I’m going to take real good care of you in just a few minutes…”
Whew…
Then there’s the NPR interview with Cookie
<interviewer> What sound do you like?
<Cookie> Nom Nom Nom Nom!
<interviewer> what proffesion, other than your own, would you least like to try?
<Cookie> (looks right at camera, googly eyes akimbo) Opthamology!
No exaggeration, that’s the funniest thing I’ve seen in months. Laugh out loud fall off my chair have to rewind the clip funny. Total anarchy in the temple of straightlaced normalcy, like Marx Bros lunacy. At times it looked like the puppeteers were doing everything possible to get Martha to kick them. Genius.
While I’m definitely a Jon Stewart fan, he basically gets to be everybody’s non-threatening liberal friend. Colbert is playing a character we should despise and still makes him charming, without breaking character (mostly). And it’s not just a matter of not knowing that Colbert the comedian is not Colbert the character, it’s a matter of actually finding the deluded, arrogant, ignorant, hypocritical, arch-conservative bloviator strangely likable.
Well said. A cult-of-personality satire. Er, a satire cult of personality. You know what I mean.
I think I’m the only person who finds Colbert completely unfunny. At least in this role.
…long lost brother?
Is this what it feels like…when doves cry?
That’s Frank Oz for sure, this time.