Final answer:
None of the historical figures listed (Nagarjuna, Vasubandhu, Dogen) were directly involved in Conze's conversion to Buddhism; the correct answer is 'None of the above'.
Step-by-step explanation:
Edmund Conze was a renowned translator and scholar of Buddhist texts who made significant contributions to the popularization of Buddhism in the West. However, the individuals listed in the provided options (Nagarjuna, Vasubandhu, Dogen) did not play a role in Conze's personal conversion to Buddhism, since they were historical figures of Buddhism who lived long before his time. Therefore, the correct answer to the question of which individual played a key role in Conze's conversion to Buddhism is: 4) None of the above.