Joe Don Baker plays a relentless and "happy in his job" killer in this film from 1973. (Yes, we are on an early seventies roll right now). Of course, it reminded me of the character in No Country for Old Men, or The Terminator, if we can fault an android for his nature. And, going back, Tommy Udo (Richard Widmark) in Kiss of Death.
There are lots of hitmen in recent movies. EW did a story on it not too long ago. But the hitman who really loves his work, like Joe Don Baker did in Charley Varrick is somewhat unusual. Or isn't it? What other ones am I forgetting?