The humans are a race native to Earth, one of the Nine Realms. Many of the Marvel Universe superheroes are humans affected by special medications, suits, radiation, ect. The humans are known to be highly weak but are suitable to be changed through special procidures. Example Captain America went through a heavy experiment to boost his strengh.
Humans in the Before Christ ages worshipped other Realms people as gods. Thor was concidered to be the god of thunder to the German North Mythology people. Out of all gods Greek gods are most popular though.