Reginald Thomas Foster OCD (November 14, 1939 – December 25, 2020) was an American Catholic priest and friar of the Order of Discalced Carmelites.

[5] Foster lived in Rome in an ascetic manner, sleeping on the floor under a thin blanket, giving away all gifts except books.

[1] In addition to his full-time work as a Papal secretary, Foster also served as a priest, tutored students, and had a weekly program on Vatican Radio, The Latin Lover.

[1][4] As a result, in November 2006 Foster founded his own free Academia Romae Latinitatis, also known as the Istituto Ganganelli, which as of 2007 was housed at Piazza Venezia in Rome.

[3] In 2008 Foster collapsed in class and had to be hospitalized; he was flown back to the United States, where he received further treatment in a nursing home in Greenfield, Wisconsin, initially on hiatus from his position.

[11] He taught Latin as a living language and influenced many Latinists;[1][12] Nancy Llewellyn was inspired by Foster to found Septentrionale Americanum Latinitatis Vivae Institutum (SALVI), the North American Institute of Living Latin Studies, in 1997, and two former students, Jason Pedicone and Eric Hewett, in 2010 revived his summer school in Rome as Living Latin in Rome, a program for college students, and have founded a non-profit organization, the Paideia Institute, which now also sponsors courses in other countries and in Greek, as well as elementary-school programs in the US.

Then, using chrestomathies of diverse Latin texts compiled by himself, Foster invited students to search for and identify the grammatical form under consideration.

He once responded to a question about Latin as a "sacred language": "In the first century every prostitute in Rome spoke it fluently—and much better than most people in the Roman Curia", and he was misquoted by the Minnesota Star Tribune as saying: "I like to say mass in the nude".