Zoe Hanna is a fictional character in BBC's medical drama Casualty, portrayed by Sunetra Sarker. She first appeared in the series twenty-two episode "Take a Cup of Kindness", broadcast on 29 December 2007. The character was a consultant in emergency medicine at Holby City Hospital's emergency department. Sarker chose to take a temporary break from the show in 2014 and Zoe departed from the show in the series 28 episode "A Life Less Lived", broadcast on 23 August 2014. She returned in the series 29 episode "Return to Sender", broadcast on 25 October 2014. Sarker later decided to leave the series indefinitely, but producers asked that she did not announce her departure in order to surprise viewers. After over 8 years on-screen, Zoe departed the series in the series 30 episode "Hello, I Must Be Going", broadcast on 7 May 2016. It was confirmed in September 2017 that Zoe would return for a single episode. She appeared in the nineteenth episode of series 32, broadcast on 13 January 2018. Sarker reprised the role again in 2023 for two episodes linked to Charlie Fairhead's (Derek Thompson) exit; they feature in series 38 and aired on the 9th and 16th of March 2024.

Zoe was described as a "maverick rebel-with-a-cause" and a "good doctor" who "knew what she was talking about" by Sarker. Sarker had portrayed nurses in previous roles who were billed as loveable, sweet girls and preferred playing a feisty character. Zoe enjoys being a doctor and prefers saving lives than working on paperwork, which influenced her decision to step down as clinical lead in 2014. Zoe's personal life is featured frequently in the series and Sarker described Zoe as "kooky" outside of work, but focused upon entering resus.

Zoe's storylines upon her introduction included an affair with married man Sean Anderson (Richard Dillane), being blackmailed for her affair with a fifteen-year-old while unaware of his age and being appointed the emergency department's clinical lead. Zoe later resigned from the post when she began struggling with the demands it involved. In 2008, Zoe became embroiled in helping Abby Evans (Amy Manson), who was being abused and when Abby was killed, Zoe fostered and planned to adopt her daughter Sharice Brooks (Adrianna Bertola). She later began a relationship with her colleague Nick Jordan (Michael French), which dissolved when she lied about being pregnant with his child. They continued a friendship and when Nick refused surgery for a brain tumour, Zoe forged his signature.

A long-running storyline for Zoe was her discovery that she was infertile, something which affected her relationship with Matt Strong (Raymond Coulthard). Zoe developed close friendships with Dylan Keogh (William Beck) and Tess Bateman (Suzanne Packer) during her time in the ED. Zoe was appointed acting clinical lead in 2012, a role which she began permanently in early 2013. She clashed with her deputy Connie Beauchamp (Amanda Mealing) over her management of the emergency department and passed over the role to her in mid-2014. Show producers created a May–December romance for Zoe in early 2014 with porter Max Walker (Jamie Davis). The relationship was well-received by viewers and was labelled "Zax" by fans. They married in 2015 which was followed by an explosive wedding reception that endangered various lives.

Actress Sunetra Sarker was cast in the role of Zoe Hanna in 2007, joining the show during the twenty-second series. Zoe was introduced as the emergency department's new consultant. Despite being the daughter of a doctor and having portrayed nurses in three of her previous roles, Sarker struggled with the medical jargon and admitted that she learns the terminology phonetically. Sarker said her father was delighted that she was portraying "a good doctor". Sarker added that Zoe's personality attracted her to the role, stating it was a "relief" to play someone feisty as she played "loveable, sweet girls" in her previous roles.

Prior to appearing in Casualty, Sarker had played a guest role in sister show Holby City. Sarker describes Zoe as: "strong, cheeky and rebellious." In 2009, during Zoe's fostering storyline, Sarker commented on her character's feelings, saying: "she felt very guilty about Sharice's mother dying and being partially to blame for it all and I think she's tried to do the right thing.". Sarker then continued, claiming that Zoe was "layered in a lot of selfishness, a lot of righteousness, a lot of pigheadedness". Later on, having given up Sharice, Zoe then embarks on a relationship with department head Nick Jordan. Sarker explained that Zoe and Nick have a very interesting dynamic" and that: "You can see that they're very similar people which would make them allies or enemies. [...] Zoe's the first female to meet Jordan's professional standards. She's no pussycat and Jordan knows that. He's got a certain amount of respect for her, as she has for him. Characterising the relationship, Sarker explained: "They've both been single for a very long time through their own choices and neither of them feel any pressure or expectations, which is a good combination for something to happen. I think this is the grown-up version of a flirtation. It's a bit more factual with these two; there isn't much softness or gooeyness to them. They are more like steel on steel!"

In 2014, series producer Erika Hossington spoke to Digital Spy about future plans for Zoe, saying that one of three standalone episodes aired by the series would be centred around Zoe, "The second standalone is an episode for Zoe, which has been written by Barbara Machin. It's a 'What if?'-themed episode." Hossington also spoke about Zoe's relationship with Max, saying that it was the light relief she needed whilst clinical lead, but when the audience began engaging into their relationship, they became pleased with the fanbase. She continued to state they are "great" together as well as comparing them to Moonlighting's Cybill Shepherd and Bruce Willis. Hossington also revealed that following their rivalry, Connie and Zoe would call a truce.

In 2012, after the characters of Sam Nicholls (Charlotte Salt) and Dylan Keogh (William Beck) were revealed to be married, Casualty producer Nikki Wilson teased Zoe's relationship to Inside Soap with Dylan saying, "The relationship between Dylan and Zoe is very interesting, because when we first mentioned the obvious chemistry between the pair to the actors who play them [Beck and Sarker], they genuinely had no idea! So in one way it's great that they're not playing it in that way. But we really enjoy their banter, and there's definitely a lot more stuff to happen between them. Whether they'll get together remains to be seen...."