Question: who is nathan riggs in grey's anatomy
[{'answer': 'portrayed by actor Martin Henderson', 'provenance': [{'wikipedia_id': '50811211', 'title': 'Nathan Riggs', 'start_paragraph_id': 1, 'start_character': 245, 'end_paragraph_id': 1, 'end_character': 280, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': "a fictional character from the television medical drama Grey 's Anatomy which airs on the American Broadcasting Company ( ABC ) in the United States"}, {'provenance': [{'wikipedia_id': '50811211', 'title': 'Nathan Riggs', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 660, 'bleu_score': 0.729282308600625, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6730063563416028641}, 'section': 'Section::::Abstract.'}]}]