For those of you not following my Tumblr, I will be uploading one of my Doctor sketches up each day leading up to the Time of the Doctor Christmas Special. Each Doctor caricature takes roughly an hour to draw from sketch to final inking. All 12 were done over the course of 3 days.
Here is the Fourth Doctor played by Tom Baker 1974-1981.
You can see all the Doctor pictures on the Regeneration Chart