Landing a plum role in Doctor Who is a once-in-a-lifetime gig for any actor. Unless, that is, you land two.

More than a few thespians have popped up in the Whoniverse on multiple occasions. Spacial genetic multiplicity? Or just a casting director playing favourites? You be the judge!

Note: We've been ruthless here, and have taken only from new Who (post-2005). We're also discounting any appearances in the extended universe/spin-offs (e.g. Torchwood). And no supporting artistes who've donned various monster costumes over the years, either!

1. Peter Capaldi

BBC

Six years before he stepped in for Matt Smith, Capaldi appeared in a David Tennant era episode – 'The Fires of Pompeii' – as Lobus Caecilius, who was whisked away from the eruption of Vesuvius in the TARDIS.

In a superbly nerdy Easter egg/fig leaf for fans, it was later revealed that Capaldi's twelfth Doctor had taken on Caecilius's appearance as a reminder to himself that saving lives should always be prioritised over preserving history. (Could have just used a Post-it note, mate.)

It's not unheard of for an actor who's previously played a supporting role on Doctor Who to later be cast as the lead: Colin Baker did the same, playing huffy Commander Maxil in 1983's 'Arc of Infinity' – just 14 months before he debuted as the sixth Doctor.

BBC

Capaldi, though, went one better, playing a third role in the wider Whoniverse: that of tortured John Frobisher in 2009's Torchwood: Children of Earth. According to Steven Moffat, Frobisher's suicide at the closure of that mini-series was time's way of "reasserting itself" after the Doctor saved Caecilius, who was, apparently, John's ancestor.

Superbly nerdy.

2. Karen Gillan

BBC

Capaldi wasn't the only future Doctor Who lead to debut in 'The Fires of Pompeii' though – funnily enough, the woman destined to become Amy Pond played a soothsayer in the same episode.

Karen's unnamed character in the Tennant episode possessed psychic powers, with an ability to "see through time" because of the rift activity in ancient Pompeii. She, of course, played beloved companion Amy from 2010-12, making a final cameo in 2013 for co-star Matt Smith's send-off.

Here though, no attempt was made to connect Amy and the soothsayer – we suppose that, what with a rebooted universe and River Song (Alex Kingston) being revealed as her time-displaced daughter, not to mention the entirety of 'The Girl Who Waited', there was quite enough timey-wimey gubbins going on in Amy's timeline as was.

Related: Every "new" Doctor Who episode ranked

3. Jennifer Hennessy

BBC

Remember Bill Potts' clueless foster mother Moira?

Hennessy appeared in two episodes of series 10 – 'The Pilot' and 'Extremis' – as Moira, but this wasn't her first venture into the worlds of Doctor Who.

A decade earlier, the actress had played Valerie, wife of Ardal O'Hanlon's feline charmer Thomas Kincade Brannigan, in the David Tennant "traffic-jam-in-space" episode 'Gridlock'.

(Bonus fact: Hennessy was also a member of the St Winifred's School Choir, who reached number one in the UK Singles Chart in 1980 with the song 'There's No-One Quite Like Grandma'. Quite the résumé.)

4. Mark Gatiss

BBC

You're probably aware that Gatiss, in addition to writing nine episodes of the series over a 12-year period, has also played both hero and villain on Doctor Who.

First was his role as the monstrous Professor Lazarus ("I'm 76 years old... and I am reborn!") in series 3's 'The Lazarus Experiment', followed by a guest spot 10 years later in Peter Capaldi's swansong 'Twice Upon a Time' as 'The Captain' (later revealed to be Archibald Hamish Lethbridge-Stewart, grandfather of the Doctor's old ally The Brigadier).

But you might not be aware of his two other roles: an uncredited Gatiss voiced World War II pilot Danny Boy in both his own 'Victory of the Daleks' (2010) and the later 'A Good Man Goes to War' (2011) and also donned heavy prosthetics to play the alien Gantok in series 6 finale 'The Wedding of River Song'.

For Gantok, Gatiss was credited under a pseudonym, 'Rondo Haxton', a reference to Hollywood horror film icon Rondo Hatton.

5. Chipo Chung

BBC

Chung played tragic, sweet-natured Chantho, caught up in the violent re-emergence of the Master (Derek Jacobi), in 2007's 'Utopia'.

Though she'd loyally served and grown close to Professor Yana, her unrequited love was quashed when Yana was revealed as merely a front for The Master. The reawakened villain brutally offed Chantho using a live electric cable, though she survived just long enough to shoot him – go Chantho! – triggering his regeneration into John Simm.

(A female Malmooth, Chantho was the last of her kind, which makes the Master's actions here even worse – he was committing genocide!)

Just one year later, Chung got to unleash her own villainous side: now sans insectoid prosethetics, she played the menacing fortune teller who manipulated Donna (Catherine Tate) in series 4's 'Turn Left'.

Related: Doctor Who losing its Saturday slot could be the best thing for the show

6. Freema Agyeman

BBC

Before she pined for the tenth Doctor as companion Martha Jones, Agyeman played the small role of Adeola Oshodi, a technician at Torchwood One in Canary Wharf, in the 2006 episode 'Army of Ghosts'.

'Adi' was snatched up and converted by the Cybermen, before being put of her misery by the Doctor, who overloaded the signal to her cybernetic earpiece.

Having recast Agyeman in a regular role for the following series, Russell T Davies inserted a line into Martha's debut 'Smith and Jones' that established Adeola was Martha's cousin. They just shared a really strong family resemblance.

7. Adjoa Andoh

BBC

Speaking of the Jones family, Martha's fiery mother also had previous with the Doctor.

Andoh appeared in seven episodes of Doctor Who between 2007 and 2008 as Francine Jones, but actually made her series debut a year earlier (though you may not have recognised her).

She was all-but-unrecognisable as Sister Jatt, one of the sinister Sisters of Plenitude, in series 2 opener 'New Earth' – having used up her nine lives, Jatt met a sticky end when she was infected with various viruses by a contagious patient at New New York Hospital.

Francine could be pretty catty, too, though, and wasn't averse to getting her claws out. *Coughs up furball*.

8. Eve Myles

BBC

Yes, she was a lead in Torchwood, but Myles's Gwen Cooper also popped up in two episodes of Doctor Who – series 4's two-part finale 'The Stolen Earth'/'Journey's End' – so this one totally counts.

It was her Who debut as Gwyneth, a kindly 19th century servant girl with clairvoyant abilities who was consumed by the alien Gelth, in 2005's 'The Uniquet Dead' that inspired Russell T Davies to cast Myles again, this time opposite John Barrowman's Jack Harkness in a new spin-off series.

Again, RTD decided to address the striking similarity between Gwen and Gwyneth head-on – though it's a common misconception that the former is the latter's descendent.

According to Davies, Gwen and Gwyneth are not related, but their resemblance is the result of something called "spacial genetic multiplicity". "It's not familial as we understand it," he said. "There's no blood tie. Spatial genetic multiplicity means an echo and repetition of physical traits across a Time Rift."

Well, duh.

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