Which MotoGP rider won the most MotoGP world championships?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'INTERNAL', 'name_': 'Q38', 'id': 0, 'label': 'Italy'}, {'type': 'INTERNAL', 'name_': 'Q965550', 'id': 1, 'label': 'motorcycle road racing'}, {'type': 'INTERNAL', 'name_': 'Q850292', 'id': 2, 'label': 'Grand Prix motorcycle racing'}, {'type': 'INTERNAL', 'name_': 'Q108032767', 'id': 3, 'label': 'Marlboro Yamaha Team Agostini'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q10858737', 'id': 4, 'label': 'MotoGP'}, {'type': 'INTERNAL', 'name_': 'Q15080981', 'id': 5, 'label': 'Francesco Bagnaia'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q253450', 'id': 6, 'label': 'Giacomo Agostini'}], 'links': [{'name_': 'P17', 'source': 0, 'target': 0, 'label': 'country'}, {'name_': 'P641', 'source': 2, 'target': 1, 'label': 'sport'}, {'name_': 'P527', 'source': 2, 'target': 4, 'label': 'has part(s)'}, {'name_': 'P17', 'source': 3, 'target': 0, 'label': 'country'}, {'name_': 'P641', 'source': 3, 'target': 1, 'label': 'sport'}, {'name_': 'P1037', 'source': 3, 'target': 6, 'label': 'director / manager'}, {'name_': 'P27', 'source': 5, 'target': 0, 'label': 'country of citizenship'}, {'name_': 'P2416', 'source': 5, 'target': 2, 'label': 'sports discipline competed in'}, {'name_': 'P1344', 'source': 5, 'target': 4, 'label': 'participant in'}]}