A headhunter is a character which appears if Geralt kills one or more mercenaries, in particular, mercenaries guarding the Inn in the Outskirts and city guards in Temple Quarter. The same model as Jean-Pierre is used, so do not be confused! He is extremely difficult to defeat and has a very tough attack.
The only reported successful method of killing him to date has been to use the same strategy that is used to kill the golem in the swamp, which is to say, the pylons and a good electrical storm. However, there is nothing to be found in his remains and a second headhunter will come for Geralt.