When Marvel's expansion made it impossible for Lee to continue writing the company's entire line of books, Lee passed as much on to Roy Thomas as he could, but still needed writers, so O'Neil took the reins for a short-term run of Doctor Strange stories in "Strange Tales," penning six issues. He also wrote dialog for such titles as "Rawhide Kid" and "Millie the Model," as well as scripting the final 13 pages of "Daredevil" #18 over a plot by Lee, when Lee went on vacation.