William Andrews Clark Jr. (March 29, 1877 – June 14, 1934) was a Los Angeles–based philanthropist and the youngest surviving son of copper baron and U.S.

In 1919, he hired bibliographer Robert E. Cowan to consult on book-buying purchases and to help with the compilation of a printed library catalog.

[4] In 1907, he married Alice McManus (1883–1916), a native Nevadan, and they moved their permanent home to Los Angeles in the early 1910s (Clark County, Nevada is named for his father).

Their house at Adams Boulevard and Cimarron Street occupied the grounds that the Clark Library is now located.

Notable among his lovers was Harrison Post, who co-transcribed Clark's collection of Oscar Wilde's letters to Lord Alfred Douglas.