 Nayler became the most prominent of the travelling Quaker evangelists known as the "Valiant Sixty"; he attracted many converts and was considered a skilled theological debater.Beginning in 1656, Fox expressed his concerns to Nayler that both Nayler's ministry, and that of his associate Martha Simmonds were becoming over-enthusiastic and erratic.Fox's concerns apparently centered specifically on Nayler's having allowed a group of his "followers" to effect that Nayler himself might in some sense be a great prophet or even a "messiah figure".