Marie Severin - Preliminary cover designs for Marvel comics, from the late 60’s-early 70’s, when she designed “virtually every cover that appeared on a Marvel comic book.”
She made them on 8 1/2x11 paper, often a piece of Marvel stationary so “the guys would know where it came from”. Both John Buscema and Jack Kirby kind of hated her sketches because they were “so good.” She would get the sketch so right that they were forced to more-or-less copy her marks and try to get the flavor of what she’d already gotten.
Many of her designs are considered to be superior to the finished covers, and she certainly had a huge impact on the “look” of Marvel comics during that time.
(via Marie Severin: The Mirthful Mistress of Comics by Dewey Cassell)