Which preposition to use with unus

in Occurrences 2%

1635Besides these the second book of the first part of the English Arcadia is said to be wrote by him, in so much that he may be accounted, says Langbaine, "if not Unus in omnibus, at least a benefactor to the public, by those works he left behind him, which without doubt perpetuate his memory."

Which preposition to use with  unus