Irvin Ungar (born 1948) is an American former pulpit rabbi and antiquarian bookseller, considered the foremost expert[1][2] on the artist Arthur Szyk.

While serving as the rabbi at Temple Sinai in Forest Hills, New York (1974 – 1980), Ungar earned his Pastoral Counseling Degree from the Postgraduate Center for Mental Health and his Master of Sacred Theology (S.T.M.)

During his seven years as a rabbi in Burlingame, Ungar also wrote opinion pieces on social and religious issues for the San Mateo County Times.

[6] In 1987, Ungar founded Historicana (known as Holy Land Treasures from 1987 to 1991), becoming an antiquarian book dealer specializing in historic Judaica.

Notable items that Ungar owned and sold over the years include Anne Frank’s “Forget Me Not” autograph inscription;[8] the original handwritten draft in Hebrew of Martin Buber’s 1939 letter to Mahatma Gandhi regarding a two-state solution in Palestine;[9] a rare Theodor Herzl autograph letter, dated November 1900, stating a plan to “bring the cause of Zionism before the English Parliament”;[10] and a letter signed by both King Ferdinand and Queen Isabella, dated 1492, on the confiscation of Jewish property and the expulsion of Jews from Spain.

Ungar's increasing interest in Arthur Szyk changed the direction and scope of Historicana in key ways.

In his new role as President of the Society, and later as Society Curator, Ungar increased Szyk’s visibility over a 20-year period through lectures, newsletters, art history papers, and exhibitions, including the traveling exhibition “Justice Illuminated: The Art of Arthur Szyk.”[24] Ungar's first public lecture on Arthur Szyk took place at Hebrew University of Jerusalem in 1994, on the hundredth anniversary of the artist’s birth.

Ungar also delivered the keynote address at the opening of “Arthur Szyk — Drawing Against National Socialism and Terror”[28] at the Deutsches Historisches Museum in Berlin, and for the opening of the “Justice Illuminated” traveling exhibition[29] at the Jewish Historical Institute in Warsaw, Poland, as part of the Arthur Szyk Society’s Renaissance Tour.

[57] Rabbi Byron Sherwin, a renowned Jewish theologian, scholar, and author, collaborated closely with Ungar on several key projects.

[17] A few months after the sale of the collection, Ungar co-published, with GILES of London, the book Arthur Szyk: Soldier in Art to coincide with the New-York Historical Society exhibition of the same name.