William David O'Brien

William David O'Brien (August 3, 1878 – February 19, 1962) was an American prelate of the Roman Catholic Church in the United States. He served as an auxiliary bishop of the Archdiocese of Chicago in Illinois from 1934 until his death in 1962, and was named an archbishop in 1953.

Early life and education William O'Brien was born on August 3, 1878 in Chicago, Illinois, to Charles D. and Alice M. (née O'Hara) O'Brien. He received his early education at John H. Kinzie Elementary School, then attended the Holy Name Cathedral Preparatory High School, both in Chicago.

O'Brien then entered St. Vincent's College in Chicago, graduating in 1899. After his ordination, the archdiocese assigned O'Brien as curate at St. Basil's Parish in Chicago. While still working for the Extension Society, O'Brien was named as pastor of St. John's Parish in Chicago in 1924. The Vatican elevated O'Brien to the rank of papal chamberlain that same year. O'Brien was named an assistant at the pontifical throne in 1947. In his later years, he relinquished the editorship of the Extension Magazine and delegated many of his administrative duties, but still closely following the society's activities and frequently visiting its headquarters.

O'Brien died on February 19, 1962, at Little Company of Mary Hospital in San Pierre, Indiana, at age 83.