Sienna Blake (also Bradley) is a fictional character from the British Channel 4 soap opera Hollyoaks, played by Anna Passey. The character made her first appearance on 21 November 2012 and was introduced as the estranged twin sister of established character Dodger Savage (Danny Mac), along with her father Patrick Blake (Jeremy Sheffield). Emily Lawrance was originally selected for the role, however Passey replaced her within weeks and only she has appeared on-screen as Sienna. The character has had a daughter, Nico (Persephone Swales-Dawson), with Dodger, and twins Sebastian and Sophie with Warren Fox (Jamie Lomas), an affair with Darren Osborne (Ashley Taylor Dawson), a marriage with Ben Bradley (Ben Richards), an affair with Trevor Royle (Greg Wood) who was later killed by Nico, a relationship with her half-sister Liberty Savage's (Jessamy Stoddart) former boyfriend Brody Hudson (Adam Woodward), and been diagnosed with cervical cancer while pregnant. Passey took a short break from the show in early 2020 and was absent between 17 January and 30 March.

In February 2024, Sienna discovers that her love rival Dilly Harcourt (Emma Johnsey-Smith) is Patrick's daughter and her half-sister. However, in the episode aired on 21 August 2024, it was revealed that Patrick was not Sienna's father; it was, in fact, his twin brother Jeremy Blake (also played by Sheffield). Sienna enters into a relationship with Ethan Williams (Matthew James-Bailey), but accidentally pushes him to his death on their wedding day, when his affair with Vicky Grant (Anya Lawrence) is revealed. Jeremy helps her conceal Ethan's murder, and he frames Dilly; Sienna discovers later that Jeremy had killed her and is a serial killer. On 22 October 2025 Sienna is one of many Hollyoaks characters that appears in the crossover with Brookside.

The character of Sienna was announced on 7 October 2012, with Emily Lawrance cast in the role, however the role was recast with Passey before the character made her on-screen debut. Sienna is the twin sister of Dodger Savage (Danny Mac), the twin sibling Dodger never knew he had. Passey made her first on-screen appearance as Sienna in the episode broadcast on 21 November 2012.

Sienna Blake is beautiful, clever and calculating, often keeping secrets from those around her. A troubled girl with serious insecurities, Sienna conceals her cold, cynical and manipulative behaviour beneath a charming, warm exterior. This conflicting personality has allowed Sienna to lure many into her web of lies and deceit...

— Channel4.com on Sienna.

In an interview with Digital Spy Passey described Sienna as a "bit of a villain" with a more "complicated" narrative. When she joined the show, Passey was disclosed the background of Sienna's character by the producers, "I knew all about her upbringing and the problems she'd had with her family." On the characters background Passey said, "She's had quite an unusual upbringing, because she's never really had any friends. Usually, most people learn how to socialise and form relationships with people as they grow up, but Sienna has missed out on all of that. She's only ever really had her father."

Passey opined that Sienna is not "evil". Speaking to Inside Soap, Passey said: "With her upbringing, she isn't an out-and-out evil person. She really believes she's got her reasons to do what she does."

On 20 May 2014, it was announced that actress Persephone Swales-Dawson would play Nico Blake, who is revealed to be Sienna's long lost daughter. Although she knows that Sienna is her mother, Sienna believes otherwise due to her being told by her father, Patrick, that her daughter is someone else. Although Sienna, initially disbelieves Nico, she starts investigating her claim after suspecting that she has something to do with Nancy Osborne (Jessica Fox) finding out about her new job, which leads to Sienna finally recognizing that Nico is her daughter.