Super-soldier Serum Recipient

It's the usual Captain America-ish story: Germans come up with serum, scientists defects and gives serum to the Allies, defector dies before he can reveal the secret of the formula. Only this time the serum isn't used much because it has a high chance of horrific mutation -- which most often results in death -- with a very low chance of super-powers (most often with horrific mutation), and the defector isn't the creator of the serum but rather of a "stabilizing agent" which is supposed to eliminate the chance of horrific mutation and increase chance of powers (his secret is not the formula for this but something else, which shall remain secret for now). The stabilizing agent seemed to work on the first subject, but on the majority of later subjects it's shown only to suppress the mutation (and even then both the horrific and powers parts). Despite the astronomically low rate of gaining anything useful the US has dusted off the serum every decade or so to try some new variant.