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Hey everyone! I have a theory about the super-soldier serum. The idea is that Abraham Erskine may have found Terrigen Crystals at some point. Then, he would have used these crystals to develop the serum that was applied to Red Skull. The serum worked, but ended up causing the deformation in his face. After that, Erskine took the project to the United States and, with the help of Howard Stark — who created the Vita-Ray chamber — managed to transform Steve Rogers into Captain America. And it wasn't just him: years later, the US government tried to recreate the super-soldier serum and ended up creating new "superhumans" without realizing it. For example: The Hulk, who basically replaced the Vita-Rays with Gamma Rays.

Spider-Man, since someone may have injected a type of serum into the spider that later bit Peter.

Matt Murdock, who was blinded as a child while saving a man from a runaway truck carrying chemicals—these chemicals may have been remnants of some variant of the super-soldier serum.

In short: the super-soldier serum may have originated from the Terrigen Crystals, and over the years it ended up creating new heroes without the government even realizing it.