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Who is Line of Duty’s Dot Cottan?

Dot Cottan in Line of Duty
(Image credit: BBC/World Productions/Steffan Hill)

Everything you need to know about Dot Cottan, Line of Duty's double-dealing Detective Inspector. Contains spoilers if you've not seen all the episodes!

Matthew 'Dot' Cottan is a key player in the world of Line of Duty.

The officer was instrumental to the first three seasons of the ever-evolving plot of Line of Duty. 

If you need a refresh ahead of Line of Duty season 6, we’ve put together a little guide that tells you all you need to know about the officer himself.

Beware! There are spoilers ahead if you’re not caught up just yet...

Who played Dot Cottan?

Craig Parkinson, who's doing a podcast alongside the new series, played Matthew Cottan in the first three seasons of Line of Duty.

What rank is Dot Cottan?

Dot started out in Line of Duty as a Detective Sergeant but he was promoted to Detective Inspector after he joined AC-12.

Why is he called Dot?

DI Matthew Cottan earned his nickname early on in service. He was named after the legendary EastEnders character, Dot Cotton.

Craig Parkinson as DI Matthew Dot Cottan in Line of Duty season 3

Craig Parkinson as Matthew 'Dot' Cottan in series three.

Why is Dot Cottan so important? Major spoilers ahead!!

In the final moments of season one, Dot brought Tommy Hunter into the back of a police van, where he told Hunter to play along with the investigation and seek immunity. Hunter, in return, referred to Dot as “the best caddy I ever had”. This was the first time we were properly shown Dot was up to no good, but it certainly wasn’t the last! 

If you haven’t seen season 2 yet, don’t read on!

Dot, now working at AC-9 in witness protection, is eventually revealed as the mastermind behind the assassination of Tommy Hunter. Hunter had previously the organised crime group but had turned informant for AC-12 in exchange for immunity.

During this investigation into Hunter's murder, Dot is formerly recruited into AC-12 by Ted Hastings (played by Adrian Dunbar). In the final episode of this season, Dot tells former TO-20 colleague Nigel Morton not to reveal knowledge of Cottan’s double-dealing. In exchange, Dot promises to turn a blind eye to Morton leaking information about ongoing investigations to the press.

Huge spoilers for season three and beyond!

In series three, Dot continuously disrupted AC-12’s investigation into the paedophile ring that involved retired Chief Superintendent Patrick Fairbank and other high-ranking officers. 

During the investigation, Dot destroyed Danny Waldron’s list of targets. He also murdered DI Lindsay Denton (Keeley Hawes) when she recovered Danny’s back-up copy. Despite helping Dot by purposefully misidentifying The Caddy, Morton eventually revealed Dot’s criminal activities to Kate off the record.

Later in the series, Dot begins framing Steve Arnott (Martin Compston) as both Denton’s murderer and as “The Caddy”. Dot’s criminal doings were thankfully put to an end in the series’ explosive, feature-length finale. Armed, he attempts to escape AC-12, with Kate Fleming (Vicky McClure) in hot pursuit.

Despite almost escaping, Dot lost his life jumping in the way of a gangster to prevent Kate from being shot. In his final moments, Dot recorded his dying declaration, giving up some key info on the group he worked for.  

Kate confronts Dot Cottan in Line of Duty.

DS Kate Fleming (Vicky McClure) confronts Dot Cottan in the finale of Line of Duty season 3.

So, why is Dot Cottan's dying declaration so important?

If you're a Line of Duty fan, there's only one question you want an answer to... who is H? 

Dot Cottan’s dying declaration revealed H to be a criminal within Central Police Service. H's identity has been the biggest mystery in the show ever since. 

Initially, corrupt ACC Derek Hilton used the testimony to accuse Ted Hastings of being H in season 4. These accusations were later dropped and Ted remained in charge of AC-12 by the end of season 4.

In season 5, we learned that H was actually four separate corrupt people, not just one person. Right now, we only know the identity of three of those moles. Hopefully, we'll get to know who the fourth bent copper is when Line of Duty returns.

Line of Duty series 6 starts on BBC1 on Sunday 21st March at 9pm – see our TV guide for more shows to enjoy. You can catch up on series 1-5 on BBC iPlayer now.