Air Carrier pilot reported stopping quickly during parking after losing sight of wing walker who had crossed in front of engine. Pilot discussed this with the offending ramp person who seemed to dismiss pilot's concerns.

Narrative

During final taxi to park our left wing walker walked with his back to the wing tip; then proceeded to cut across the safety area in front of the number 1 engine and then continued to cut in front of the nose of the airplane. I was taken by surprise as I was focused on the marshaller. I had to stop the airplane quickly when I saw this person disappear under the nose. I opened my window to communicate directly with the marshaller about where our left wing walker went. We were only 10 ft or so from the final spot and when I was satisfied the area was clear we continued to finish parking. The left side wing walker left his post and then crossed in front of a moving airplane! I've never seen such disregard for the safety area or the job of a wing walker. I went down to the ramp to speak with this individual and all he told me 'not to worry I stayed clear;' and that he didn't appreciate me yelling at him. I was talking in a raised voice because it was loud. I informed him that he left his position as the wing walker and cut us off and how unsafe it is to go out of view of the flight deck. He was not receptive to my comments and didn't seem to care about the rules. Report submitted with names.Cause:--I don't know if it's complacency or just willful disregard of procedures. But reevaluation of training and safety procedures a must.