c. 1300, patroun, "a lord-master, one who protects, supports, or encourages," also "one who has the right of presenting a clergyman to a preferment," from Old French patron "patron, protector, patron saint" (12c.) and directly from Medieval Latin patronus "patron saint, bestower of a benefice; lord, master; model, pattern, example," from Latin patronus "defender, protector; former master (of a freed slave); advocate," from pater (genitive patris) "father" (see father (n.)). A doublet of pattern (n.); also compare patroon.
From late 14c. as "founder of a religious order," also "a patron saint." The meaning "one who advances and encourages the cause or work" of an artist, institution, etc., usually by means of the person's wealth and power, is suggested from late 14c., clearly in this sense by c. 1600; "commonly a wretch who supports with insolence, and is paid with flattery" [Johnson]. The commercial sense of "regular customer" is recorded from c. 1600. Patron saint "saint regarded as a special protector of a person, place, profession, etc." (by 1717) originally was simply patron (late 14c.).