By 1651, Backhouse had become the mentor of English antiquary Elias Ashmole. It is not clear at which date they first became acquainted, but Ashmole records, in a diary entry of April 1651, that "Mr Will: Backhouse of Swallowfield in Com., Berks. caused me to call him Father thenceforward." This diary entry is Ashmole's earliest mention of Backhouse, but such an intimate connection between the two would suggest they had known each other for some time before this point. In 1644, Ashmole had first begun his interest in astrology and, by the 1650s, Ashmole devoted much of his time towards the study of alchemy, and collection of alchemical MSS. By 1648, Ashmole had become lord of the manor at Bradfield, which happened to be in the immediate neighbourhood of Backhouse's Swallowfield. The following relationship has been described by C. H. Josten as having an effect on Ashmole that "cannot be overrated".
