I'll guess that it's the 'Parker' from the Westlake/Stark series of books. One of the early ones was filmed as Point Blank with Lee farking Marvin. Cracking stuff.
The best one as far as closeness to the books is The Outfit with Robert Duvall. Physically, I can't see him as Parker, but emotion wise he's spot on. It's the best of the Parker adaptions. Physically Marvin and Gibson were the best.
I rate the adaptions -
1) The Outfit
2) Point Blank
3) Payback - Director's cut. It's a much darker film in that version.
4) Payback - Standard version.
5) Parker
6) Slayground
7) The Split

Made in The USA
I haven't seen a copy, but Mise à Sac, based on The Score, and filmed in France is said to be a very good film.
Here's a good scene from The Outfit. A new clean copy was put on the market about a year ago, and it's well worth the watch -
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