Marcus Dean is a fictional character from the British soap opera Emmerdale, played by Darcy Grey. The character and casting were announced in January 2022, with Grey making his first appearance as Marcus on 3 February 2022. Grey was happy to be cast on the soap and believed that he and the character shared many similarities. Marcus was introduced as the estranged son of former character Pierce Harris (Jonathan Wrather) after being contacted by Pierce's former wife, Rhona Goskirk (Zoë Henry). Marcus' arrival initially causes issues for Rhona and her relationship with Marlon Dingle (Mark Charnock). Following Pierce's death, Marcus begins a romance with Ethan Anderson (Emile John) and decides to remain in the village. Rhona initially does not want Marcus to stay but changes her mind when she realises that he is not like his father. Marcus and Ethan's relationship strengthens and the two move in together.

Marcus is later sexually harassed by Ethan's boss, which puts a strain between the couple. In early 2023, it was announced by Emmerdale producers that Ethan and Marcus' relationship would end in order to create new storylines for Ethan's family. Shortly afterwards, it was announced that Grey would be departing the soap as Marcus in order to explore new acting roles. Marcus ends up cheating on Ethan which leads to their breakup, and he departs the village shortly afterwards. For his role as Marcus, Grey was shortlisted for the 2022 British Soap Award for Best Newcomer. Marcus received positive reception when he debuted on the soap, and several critics have noted the resemblance between Marcus and Pierce. Critics initially praised Ethan and Marcus' relationship and believed that they were a strong couple. However, Marcus' cheating and his low-key departure were criticised, with some believing that the character had more potential.

"For Marcus, the battle of being torn between wanting to forget his relationship with his Dad but also ultimately, wanting to simply be loved is a challenge many of us face, and one that I hope I can bring some truth to. He is such an open book, with such an uncertain future that I just can't wait for you all to see where his journey in the village takes him!"

In January 2022, it was announced that soap newcomer Darcy Grey had been cast on Emmerdale as Marcus Dean, the son of former character Pierce Harris (Jonathan Wrather). Speaking of his casting, Grey revealed that he was "quietly smiling inside" when his agent sent him the role of Marcus, explaining, "We share so many similarities, both the good – and perhaps – some of the bad! I thought, 'I know who this kid is'. To then get the call to say that the role was mine was one of those pinch-yourself moments we actors simply dream of". Grey explained that Marcus likes to think that he is not like his father at all. Grey made his appearance as Marcus on 3 February 2022.

Emmerdale producer Kate Brooks was "delighted" to welcome Grey to the cast and believed that Marcus would make "quite the impression" on the other characters and viewers. Brooks added, "Marcus' arrival will certainly ruffle a few feathers and flutter a few hearts in the village. However, people will soon realise there's more to Marcus than merely being the son of Pierce. But will our villagers give him a chance, or will he be forever doomed to live in the shadow of his father's heinous crimes?" It was reported that Marcus' arrival would cause trouble for Pierce's ex-wife, Rhona Goskirk (Zoë Henry), who he raped. Jane Hudson, the soap's other producer, teased that viewers would have to "wait and see whether Marcus is a chip off the old block or whether he's the polar opposite of Pierce." Justin Harp from Digital Spy reported that the storyline would be "gripping" and revealed that the memories of Pierce would come "flooding back" for Rhona when she meets Marcus. Harp noted that Marcus is "suave and handsome with a penchant for brooding" just like Pierce, but questioned whether there were more similarities between the pair. Craig Jones from Yorkshire Live believed that Marcus' arrival would cause "heartache" for "village favourite" Rhona. Mike Bedigan from the Belfast Telegraph believed that Marcus' arrival would be a "shock" and questioned whether Marcus would be given a chance to be more than Pierce's son or live in the "shadow" of his crimes.

Marcus is an electrician. Grey believed that Marcus is an "interesting" character and called him "a bit of an outcast" who does not know necessarily what his position is. Grey believed that Marcus is a bit of an outcast due to having that pressure from his father, who left when Marcus was very young and thus he grew up without a clear path. Grey added that Marcus' arrival in the village is an "exciting" time of the character's life due to it being an "open book" of where Marcus' next stage in life will be. Grey also teased that viewers would see that Marcus is a bit similar to his father later on. Carlo Simone from The Argus speculated that the character would make a bit of "disruption".

Speaking about Marcus' debut, Emmerdale producer Jane Hudson revealed, "When we meet Marcus, we don't know who he is but then we find out he is Pierce's son. Pierce has written to Rhona asking to find his son, who she didn't know about." Rhona initially tracks Marcus down to tell him that Pierce is dying. Grey told Radio Times that he found it interesting that this changes what he thought was his "calm life", explaining that Marcus has "got himself a job, he knows where his mum lives and he thought he knew where he was, and then all of a sudden this piece of information comes through about his dad and it's just shifted things and reverted it back to this unstable position for him". When Rhona meets Marcus, she questions whether she can let Marcus into her life due to her dark memories of Pierce. Rhona also considers whether this could affect her new relationship with Marlon Dingle (Mark Charnock). Marcus tells Rhona that he has his own stories of his upbringing under Pierce. It is explained that Marcus has not had any contact with Pierce since he was young as he was abusive to Marcus' mother. Marcus tells Rhona that he discovered what Pierce did to her when he read it in the news. Hudson explained that when Marcus arrives at Rhona's door, she makes the "wrong" decision and decides not to tell Marlon. Rhona's close friend Vanessa Woodfield (Michelle Hardwick) is not happy about Marcus' arrival. Marcus then asks Rhona if she will visit Pierce with him, which leaves her stunned. Rhona later encourages Marcus to stay in the village after realising that he is nothing like Pierce. Marcus ends up making friends with several residents and helps out with electrical problems in the local cafe.

Prior to the character's debut, Hudson revealed that Marcus would have a "blossoming romance" with another character. Dan Seddon from Digital Spy joked that Marcus would "flirt his way" around the village. Marcus' love interest is revealed to be Ethan Anderson (Emile John). Pierce later dies and following his will reading, Marcus feels that there is no longer any point in staying in the village. Ethan asks Marcus to meet up before he leaves twice but is rejected both times by Marcus. However, Rhona and Marlon then give Ethan their approval to pursue a romance with Marcus, so he asks him out again, which he accepts. After a few months of dating, Marcus and Ethan "strengthen their bond" by deciding to move in together. This happens when Marcus helps Ethan move into a shared house, which leads to the couple growing closer and discussing their future. They decide that living together is the "natural" next step in their relationship and thus Marcus also moves into the house share. The following month, Marcus helps Ethan track down his missing sister, Naomi Walters (Karene Peter), which Ethan is thankful for.