Way back in 1961, Stan Lee was beginning the "Marvel Age of Comics". With the Fantastic Four he had established his mode of doing heroes, not just with personalities, but flawed personalities at that. Jack Kirby was his perfect partner to draw these cosmic misfits who became true dynamic heroes.
In his next endeavor to place human foibles into a person with greater physical abilities, he wanted to really tip the scales. Adding the angst of a misfit teenage science nerd, orphaned and being raised by his elderly aunt and uncle, he was really pushing super-heroes to the human side.
Stan and Jack had a story meeting about the new hero and Jack came up with a few pages of art, but it just wasn't quite right. For all of young Peter Parker's weaknesses as a human being, Jack's style just naturally imbued Spider-Man with a little too much dynamic heroism.
Stan turned to Steve Ditko.
Steve is a cartoonist who draws the everyman better than almost anybody. They look frail and strong at the same time.
That is Spider-man.
Steve Ditko is a recluse of sorts. He does occasional comic book work still, but he hasn't done an interview or had his picture taken for about 40 years. He says his work is what's important. Let the work speak for itself.
So I will. Here's a feature about Spidey that Steve drew for Spider-Man Annual #1:
Another feature about how Stan and Steve do the comics they did. Pure bullshit. Pure fun.
While Jack Kirby did the art for a great number of the early Marvel heroes, Steve did help create one other major player...and I could NOT imagine this character at all in the hands of Kirby. Kirby was science, Ditko was magic.
The other dimensions that Dr. Strange would travel through and the magic he performed, could only have been actualized by Steve.
Here's Doctor Strange's first appearance, from Strange Tales #110: