American Equivalents to The Doctors

So I was talking to a friend about Bill Nye the Science Guy earlier, and it made me realize how much he reminds me of The Doctor, well more descriptive the 11th Doctor. The quirky attitude, the cheerfulness towards children, the cool bowtie, it just seems to work.

Also Mrs. Frizzle from the Magic School Bus makes a very interesting comparison with River Song.

So companions, if you had to recast the entire show with American pop-culture characters, who would play what?

Sorry if this has been posted before, I haven't lurked this board much lately. :(