Frank R. Paul, the definitive pulp scifi artist, did the cover of the first-ever Marvel Comic in 1939. This is because Marvel’s comic books were an extension of their already existing pulp magazine publishing empire. 

Marvel Magazines (Timely Publishing), founded by Martin R. Goodman, knew Frank R. Paul as he illustrated the cover of many of their pulp magazines, like Marvel Mystery Stories and Marvel Science Stories as far back as 1938. Marvel Comics started off as an extension of the pulps into a new medium, hence why they called the most famous 20s-30s scifi artist of all time, with whom Marvel Magazines had a strong working relationship. 

Frank R. Paul’s cover for Marvel Science Stories, a year before:

Martin Goodman, pulp publisher and the founder of Marvel Magazines in the late 30s, was Stan Lee’s uncle by marriage, and gave Lee his first job in comics writing text stories in Captain America #3 (1942). Goodman had tickets on the Hindenburg’s final explosive flight (two years before creating Marvel’s comic publishing division), but had to cancel at the last minute. Incidentally, I am always amused by pedants who insist that Marvel “was actually called Timely Publishing in the 1930s-40s.” Technically true, I guess…but they were known as Marvel Magazines as far back as the 1930s.  

Here’s more support for the idea that Marvel Comics grew out of the Marvel pulp publishing empire: notice that in the first-ever Marvel Comic, they mention “Ka-Zar” on the cover as if the audience should know who he is. And they did! Marvel created that character in 1937, 2 years before Marvel even started publishing comics at all, in a character pulp in imitation less of Tarzan than of the Ki-Gor series.

Many know of Ka-Zar and the Savage Land because he was, like Captain America and the Human Torch, a pre-existing hero who was revived in the 1960s. The really unusual thing is that Ka-Zar was revived in the pages of X-Men, and so was absorbed into the cast of that title and never really broke out as a solo star, though every 2 decades, he gets a solo series.