Paul Reuben stopped by Jimmy Fallon's show to promote "Pee-Wee's Playhouse The Complete Series" out on DVD and Fallon enlisted Reubens to record a voice-over for the new Avengers movie trailer. Apparently Fallon has done this on his own before (see 'The Dark Knight Rises' trailer voice-over below)!

Here is the original Avengers trailer:

Watch Jimmy Fallon's voice over of 'The Dark Knight Rises'