Butler: the chief manservant of a house who has charge of other employees, receives guests, directs the serving of meals, and performs various personal services
In hindsight (much, much, much later), they realize that none of them had known exactly what it had taken for Tony to put Jarvis' matrix, his mind, into the shell. But in the moment? No one considers it.
The body they steal from Ultron is a husk, empty and without life. Tony understands immediately what might happen (eventually) if he is to put his friend into that husk. If he is to bring this body to life. Bodies… well, they have an unfortunate habit of dying. Android or human, it doesn't make a difference. Tony is no fool. He knows that if this being dies, Jarvis dies (again) with him. Tony won't be able to bring him back.
But that's a selfish thought, and Tony is trying to be selfless. He's trying. He really is. Doing this is their best chance of ridding the world of Ultron.
So when Vision wakes and the process is done (over with, finished, permanent), Tony just feels numb. He knows that his expression looks just as cautious, just as skeptical, and just as on-edge as the rest of them, but he is none of those things. If he weren't so in shock due to what he'd just done, he might be furious with himself.
When it, Vision, lifts Mjolnir Tony isn't surprised. Thor gives him an awkward smile and thumps him on the shoulder, obviously inferring that whatever made Vision worthy somehow, someway came from him. Tony, fortunately for Thor, doesn't have the energy to feel insulted by the obvious doubt in his smile.
Because he knows better.
Vision isn't worthy because of him; he's worthy because of Jarvis. Not J.A.R.V.I.S. That's an equally false assumption. The emphasis in the acronym had always been on Another.
Tony remembers the man well, which he considers a very fortunate thing.
"I am not Ultron." Vision pauses, looking around at them. "I am not Jarvis, either."
No, Tony thinks, you're not. He speaks and sounds like the man, sure. But the world is full of phonies and Tony knows that he will never relate to this one like he related to his A.I. He leaves the impromptu, accidental meeting feeling absolutely gutted.
Pepper is able to reassure him that his memories of his old butler are what mean the most in the end. Not J.A.R.V.I.S and not Vision. His memories reflect the man himself like nothing else ever will. Tony is able to at least maintain a professional relationship with Vision after that, but there will always be an undercurrent of tension between them, as well as a big fat line that will never be crossed.
Vision does what he was made to do, at least. Ultron never stood a chance.
In hindsight, Tony realizes he had been the only one to believe that victory would be a certainty. He also decides to never base any future A.I.s on actual people, because honestly? He never wants to go through that again.
