A patron is someone who assists someone-else who is normally of an inferior rank or experience in furthering their craft. Examples would include rich men supporting the work of specific artists and craftsmen, and experienced soldiers, merchants, craftsmen, bureaucrats and the like offering advice and preferment to selected juniors in their craft, art or speciality.
Generally, in period, a patron would either take the craftsman into their household, pay for the living of that person (which could range from humble to luxurious) for a contracted span of time, or simply contract a number of artwork or services from that person. The artist or craftsman being patronised would dedicate all their work to him/her in the first place, would allow him/her first (and sometimes sole) pick of their work, and would where necessary ascribe their success solely to their patron within the contracted span of time.
Similarly the selected junior who had received preferment was, from then on, expected to do all he or she could to support their patron's position, including spying on their behalf upon other craftsmen, undertaking work for them, and in the extreme accepting blame for their patron's errors.