Comedic Actor Matt Lucas recently announced that his character, Nardole, introduced in last year's Doctor Who Christmas Special, The Husbands Of River Song, Is set to appear as a Regular in Doctor Who series 10, airing sometime in 2017.
Here are more guest characters who should make a return appearance:
1. Nasreen Choudhry (Meera Syal), The Hungry Earth/Cold Blood, S5, E8 & 9
Nasreen, played by Meera Syal, appeared in the two part episode The Hungry Earth/Cold Blood, notable for featuring the return of the Silurians, not seen since The Fifth Doctor story Warriors Of The Deep in 1984.
Nasreen quickly formed a rapport with The Doctor when she accompanied him into the Silurian City to rescue Amy, Elliot, and Mo.
Will She Appear Again?: It's possible. Nasreen chose to enter a 1000-year stasis with the Silurians at the episode's conclusion, to be with Tony, The man she loved. If a sequel story were to take place, she could provide a link between Humans and Silurians.
2. Sally Sparrow (Carey Mulligan), Blink, S3, E10
Sally Sparrow, played by Carey Mulligan, starred in Blink, the first episode to feature the now iconic Weeping Angels. With The Doctor and companion Martha both trapped in the past, The character of Sally drove the episode's plot.
Will She Appear Again: Sadly, this seems unlikely, now that Carey Mulligan's film career is taking off.
3. Captain Henry Avery (Hugh Bonneville), Curse Of The Black Spot, S6, E3
Captain Henry Avery was mentioned briefly in First Doctor story The Smugglers, before making a physical appearance in Curse Of The Black Spot, where The Eleventh Doctor finds he and his crew being terrorized by a Siren.
The Siren is later revealed to be the medical program of a spaceship. Henry agrees to pilot the ship so that The Siren can keep his seriously ill son, Toby, alive. Captain Avery and Toby later made a cameo appearance in A Good Man Goes To War.
Will He Appear Again?: Not terribly likely, but still possible, especially now that actor Hugh Bonneville is free from Downton Abbey.
4. Jenny (Georgia Moffett), The Doctor's Daughter, S4, E6
Jenny is the daughter of The Doctor, born fully grown after his hand is forced into a Progenation Machine. She was seemingly killed taking a bullet for The Doctor, but awoke alive and well soon after his departure, stealing a space pod and taking off to see The Universe.
Will She Appear Again?: Maybe. Steven Moffatt was the one to request that Jenny survive at the end of The Doctor's Daughter. With Series 10 to be his swansong as show runner, now could be the time for Jenny to make a comeback.
5. Lorna Bucket, (Christina Chong), A Good Man Goes To War, S6, E7
Lorna Bucket was a girl from a peaceful area known as the Gamma Forests, who joined the Clerics of The Silence in the hope of seeing The Doctor again after briefly encountering him as a child.
She later turned on the Clerics in order to warn The Doctor's allies about Madame Kovarian's trap, but was sadly killed in the battle that followed.
Will She Appear Again?: Unlikely, since it was strongly implied that her earlier encounter was also with the Eleventh Doctor.
6. Psi (Jonathan Bailey) and Saibra (Pippa Bennett-Warner), Time Heist, S8, E5
Psi, a man with a computer for a brain, and Saibra, a woman with the ability to take on the appearance of anyone she touches, were recruited by The Doctor for an attempt to rob The Bank Of Karabraxos.
Will They Appear Again?: Maybe. They both survived the episode, and left The Doctor on good terms.
7. Perkins (Frank Skinner), Mummy On The Orient Express, S8, E8.
Perkins was an engineer on the space-train Orient Express. He proved a useful ally in the battle against The Foretold. The Doctor was so impressed that he offered him a place on The Tardis, though Perkins kindly refused.
Will He Appear Again?: Unlikely. It could be quite difficult to find an episode where he would fit.
8. John Riddell (Rupert Graves) and Queen Nefertiti (Riann Steele), Dinosaurs On A Spaceship, S7, E2
John Ridell, a big game hunter, and Nefertiti, an Egyptian Queen, tag along when The Doctor decides the mission to investigate an old Silurian spacecraft calls for a gang.
Will They Appear Again?: Maybe, if Rupert Graves can fit it in around his Sherlock commitments.
9. Wilfred Mott (Bernard Cribbins)
Wilf, the grandfather of Tenth Doctor companion Donna Noble, made multiple appearances, between 2008-2010. The most notable of these would be taking on the companion role himself in The End Of Time, the Tenth Doctor's final adventure.
Will He Appear Again?: Unlikely, but not impossible.
10. Stormageddon, Dark Lord Of All, Closing Time, S6, E12
Stormageddon, also known as Alfie Owens, was the son of The Doctor's former roommate, Craig. He played a vital role in defeating the Cybermen, his cries causing Craig's Fatherly instincts to overpower their Cyber Converter.
Will He Appear Again?: Probably not, but we can dream, can't we?
Anyone I've left out? Leave them in the comments!