Agent 47 has had the same actor for 25 years, and he says he's a "very, very close friend" of Hitman

gamesradar.com:

Hitman's protagonist Agent 47 has been switching disguises and targets for 25 years, but one thing has always remained constant: his voice actor. David Bateson has voiced Agent 47 since the beginning, and in a recent interview with Play Magazine, he outlined how it all started.

"I was in a studio doing a corporate thing. And that studio was also making the graphics for the first game. They actually interrupted my session. They opened the door and said 'David! Listen, if you get a minute afterwards, could you come in and have a look at the graphics of this computer game we're developing? We need a voice. We've got a character, but we don't know what he should sound like'. I went 'ok, yeah, sure'. I noticed a striking resemblance to myself right there. It was the look of that first game. Very kind of Film Noir, long shadows, like The Third Man. My favorite film is Blade Runner, and it had that kind of Blade Runner look, so I gave it a crack."

25 years is a long time to play the same role, and it's only natural to build a connection. It's hard not to become protective over the character, watching how they are received by the public with every new installment. Bateson goes on to say "I truly look upon Agent 47, Tobias Rieper, as a very, very close friend. I feel very protective of him. I feel like I really, really know this character. After so many years, both the writers and myself have kind of grown up with this character."

Of course, Agent 47 is not like many other characters. He was designed to be a blank slate, to fit into any role or disguise in broad daylight. The personality and funny dry delivery come from Bateson's familiarity with the character and the writers building him in tandem. 

"So they're writing with a knowledge of how he would say things, and what he would say. And they're also hearing me, how I would probably give an interpretation. It's become a kind of synergy of my acting talent and their writing talent., which has just got tighter and tighter."