Bourne series, what exactly was done to Bourne?

I’ve seen the movies but I don’t recall what the reveal was about Bourne, there were hints he was altered somehow medically? The Legacy movie seems to drop similar hints talking about brain tissue etc.

Was there any reveal like that?

Well, I think that he submitted to intense brainwashing and drugging. It made him follow orders, I think, and included him killing some random dude that he didn’t know.

Deep brainwashing, torture and drugging, to the point of nearly destroying his original personality, and implantation of their own construct, trading out social skills and sanity for some truly astonishing spy skills.

It’s unclear how much the brainwashing “made” him follow orders. He volunteered for it, and the guy he executed a guy (who he knew absolutely nothing about other than they told Bourne to kill him) was before he got into the program and was brainwashed, drugged or whatever else. It was proof of his dedication.

Correct me if I’m wrong, but I don’t believe that Jason Bourne was subjected to genetic engineering like Aaron Cross was. True?

True. That was a new twist in the fourth movie.