Pat O'Brien, a man of Irish descent, despite being born and raised in the United States, earned the nickname "Hollywood's Irishman in Residence" due to his frequent portrayal of Irish immigrants. Alongside close friends James Cagney, Allen Jenkins, and Frank McHugh, he was also referred to as "The Irish Mafia".
As a young boy, O'Brien was deeply devoted to the Roman Catholic faith and considered pursuing a career in the priesthood by attending the seminary. However, he never followed through with this aspiration and instead chose to pursue a career in acting, often playing characters such as Father, Monsignor, or Bishop.
Despite never having had a discernible Irish accent in real life, O'Brien was skilled at adopting a thick brogue when required for his roles. Throughout his acting career, he excelled in benevolent characters, but also demonstrated his range by convincingly portraying wise guys or con artists.
O'Brien was a highly popular film star during the 1930s and 1940s, and went on to co-star in nine films with James Cagney, including his final screen appearance in the 1981 film Ragtime.
