The character, Sully Sullivan (James Woods ) is loosely based on Boston's infamous gangster, James "Whitey" Bulger. In the series, Mickey Donovan was a consultant in a film called "Black Mass", the same name of Bulger's real-life biopic starring Johnny Depp.
Ted Levine is playing the owner of Buffalo Bill's casino. A great homage to his character of the same name from The Silence of the Lambs (1991).
Calabasas, where Ray Donovan and his family make their fictional home, is a California community, where many A-list celebrities such as Will Smith, Cameron Diaz, Jennifer Lopez, Britney Spears, the Kardashians, Kanye West, Tori Spelling, Richie Sambora and Nikki Sixx make their real-life home.
Liev Schreiber and Susan Sarandon (who joined the show for season five in 2017) appeared in Twilight (1998).
In the show, Terry is oldest brother. In actuality, Liev Schreiber is eight months older than Eddie Marsan.
The second season featured Brent Spiner as Ray's psychiatrist and Wendell Pierce as Mickey's parole officer.
Hank Azaria (Ed) and Jon Voight (Mickey) were both in Uprising (2001), a 2001 TV movie documenting the Warsaw Ghetto uprising.
The third season has Aaron Staton as Bridget's teacher, Ian McShane as Malcolm Finney, and Bronson Pinchot as a television talk show host.