I'm trying to identify a novel or novella that I read sometime before the 1980's. The key plot point was that a superhuman "government agent" was trying to capture an alien whose name was "Snipe"(?).
The super-spy had been "modified" and was one of a pair of twins (where his twin had numerous congenital deformities).
The alien had landed on Earth and was very violent, but from his perspective, was very honorable.