John Seven is an agent of Z.O.M.B.I.E.
We are given a lot on information on the concept of the organization with the very unusual and quite eye-catching name, all in the blurb for each of the adventures:
"It is the early 1960s. A secret war is being waged within the Cold War between the agents of Z.O.M.B.I.E. (Zero Organic Members of the Bureau of International Enforcement) and its rival, P.U.R.I.T.A.N. (The Peoples Union for the Reclamation of International Terror, Anarchy and Nihilism). These opposing Deep States contend for global power by any means possible -- even weaponizing the newly dead. Z.O.M.B.I.E. wishes to preserve the autonomy of nations to decide their own destiny; P.U.R.I.T.A.N. wants to cause chaos and anarchy as a pretext to bringing about their own order at the cost of jackbooted tyranny.
"Agent John Seven is one of Z.O.M.B.I.E.'s newest weapons: a 'Zero agent', a man brought back from the dead to serve his cause unquestioningly, without pain, without hesitation, without end. He is built to be a machine, but Seven is plagued by dreams and images of a life he once had. Weaponized corpse to some, zombie to others, his mission objectives also include suppressing an appetite for human flesh."
Even without the information above, we would have known something was 'different' with Seven when in the opening lines of the first recorded adventure, as he sat for too long awaiting a rendezvous and spent the time studying the rats scurrying about the Budapest apartment, he reminded himself that his trainers had pounded into him to not empathize with things like vermin and "only to identify with humans". Seven admits he often found that difficult. Seven had once been human, of course, but then he died and now that he has been reanimated, the use of the word 'human' ceased to be so accurate; humanoid, perhaps.
To assist the Zero agents in understanding details vital to their mission, they are given capsules with could impart "all kinds of select knowledge or skills from individuals whose brains were distilled, though it did not last beyond a few days". That distilled part is a touch icky, especially when we learn Seven had been told that he "could eat someone's brain and gain that knowledge direct" though his handlers forbade that.