Brennan initially appeared as Doug in the programme's online spin-off series Hollyoaks: Freshers, before his debut in the main show on 13 September 2010.

His storylines have included drug dealing, a relationship with Jenny (Daisy Turner) which ended in her murder at the hands of a serial killer, an attempted suicide, and entering a civil partnership with Ste Hay (Kieron Richardson).

[2] Channel 4's cross-platform commissioner Jody Smith told Alistair Houghton from the Liverpool Daily Post that the series would depict the new characters' "back stories and journey to Hollyoaks".

[3] Doug is Brennan's first television role; he auditioned in April 2010 after completing a degree at the Central School of Speech and Drama.

[4] Brennan told Daniel Kilkelly of Digital Spy that he knew Doug would just be a "catalyst for changes" in other characters storylines.

[6] Series producer Paul Marquess told Kilkelly that his team thought Doug was "great" and "brought a very different flavour".

[9][10] Brennan told Kilkelly that Doug is a complicated person who changes over time - he is not a very good drug dealer and makes the wrong choices.

Brennan felt that Doug's do-gooder actions are always based on the fact that he had hurt others and made the wrong choices.

[5] A man with "more barriers on the surface"; he was no longer the character who hooked up with ladies, "bragged, [...] made terrible decisions and was self-obsessed".

[12] Brennan has an American accent which altered due to differing inflections, a trait which he felt fitted in with Doug's backstory of travelling abroad.

[4] Brennan told a writer from Heat that Doug's wardrobe consists of a collection of "itchy Christmas jumpers" and chinos.

Doug "has a list of suspects" and attempts to find out who attacked him; but ends up discovering a secret about Kevin Smith (Cameron Crighton).

She begins to scam Warren Fox (Jamie Lomas) but instead decides to meet up with a man from an internet dating site.

We knew that we had a very small window of time to make it seem like we had a significant backstory, and I was lucky that Daisy was so giving as an actress, as we immediately had chemistry".

[11] On 29 November 2011 it was announced that Steph Roach (Carley Stenson) would return as part of a "Doug-centric episode" as a spirit when Doug "starts to feel lonely and depressed" in the lead up to Christmas and begins questioning whether his life is worth living.

[19] Brennan told Alison Slade from TVTimes that Doug wants to "regain control of his life" after seeing Ste and Adam on their date.

[21] Richardson told a writer from TV Buzz that Doug and Ste would not solely be "another love story" because Brendan will be involved.

[12] Doug takes fellow students Charlotte Lau (Amy Yamazaki), Jamil Fadel (Sikander Malik) and Dave Colburn (Elliot James Langridge) to France.

Doug kisses both Jem Costello (Helen Russell-Clark) and Leanne Holiday (Jessica Forrest) and starts dealing drugs for Brendan Brady (Emmett J. Scanlan).

The plan fails and Jenny arranges a date with Silas Blissett (Jeff Rawle), who she intends to drug and steal from.

Seth Costello (Miles Higson) confides in Doug about his father Carl's affair with Mercedes Fisher (Jennifer Metcalfe), behind Riley's back.

Walker (Neil Newbon), an undercover police officer, convinces Doug to help him find evidence on Brendan.

Doug fails at first, but tricks Brendan into admitting that he killed Danny Houston (Darren Day) to protect Ste.

Ste is run over by Maddie Morrison (Scarlett Bowman) after saving his adoptive daughter Leah Barnes (Ela-May Demircan).

Doug wants to use some money from the deli to pay Jim's fee, but Ste is against the idea, convinced that it would be better to let him fight his own battles.

At the leaving party, Sinead O'Connor (Stephanie Davis) brings back a bag from which she stole from Trevor thinking it's full of cash to give to Doug and Ste as a leaving present, but she is unaware that it's actually a bomb set up by Clare Devine (Gemma Bissix) to kill the McQueens at Mercedes' 30th birthday party at The Loft.

Gaining consciousness, Doug helps Sinead out of the collapsing building and she tells him that he is bleeding but he ignores it and goes back in for Ste.

Six years later, Ste went to stay with his parents before going to Newcastle after being freed from the hands of Stuart Summer and Jonny Baxter and their far-right extremism and being shunned by the entire village including his friends and family.

[4][10] Anthony D. Langford from AfterElton praised Doug's friendship with Riley, Ethan and Noah Baxter (Law Thomson).

The writer opened that Doug and Ste's "long-awaited first kiss" was "pretty hot stuff" and continued in hailing them as "Hollyoaks' hottest new couple".