5 times Doctor Who broke the boundaries with its cast

Doctor Who would be nothing without his companion, usually an earth-born assistant to offer a little bit of humanity to the Time-Lord's (or lady's) adventures through time and space.

Jodie Whittaker was recently announced as the 13th Doctor Who, but now rumours suggest actor, singer and game show host Bradley Walsh will be joining her in the TARDIS as her companion.

It's not the most obvious choice, but Doctor Who has never been known for being obvious. Here's five times the show broke boundaries with its casting and its characters in recent memory.

John Barrowman first appeared as Jack Harkness during Christopher Eccleston's short-lived time in the TARDIS. His character was introduced in 2005 and proved so popular he eventually led Doctor Who spin-off show Torchwood.

Jack was the first openly "omnisexual" character to be seen in Doctor Who and brought the first major LGBTQ+ storylines to the show.

"What I love about Jack is that he’s not a stereotype," said John Barrowman in an interview with The Telegraph in 2011.

"Jack is omnisexual, but people who watch this series will think he’s completely gay because he only has sex with men."

Jack Harkness appeared on screens for six years between 2005 and 2011 but his adventures continue, with Torchwood since being written as BBC radio plays.

Doctor Who fans don't have a problem with an alien flying through space and time in an old-fashioned police box, but the thought of a female star was too much for a small number of viewers.

The announcement was met with inevitable grumblings from some people on social media, but luckily Jodie says she was oblivious to any criticism.

"I've missed a lot of the fun stuff and probably the bad stuff because I'm not on any type of social media and never have been," the actress told Shaun Keaveny on 6 Music.

"So if I get something it's a mate screen grabbing something and sending it to me."

However, she added that the response from most fans had been overwhelmingly positive before her turn as the Time-Lady begins.

"I feel like I'm immersing myself into a world that is just – I haven't even done it yet, but the fans are the most kind and creative and enthusiastic people," she added.

"It's so exciting to be a part of that. There are only a few people who know what it's like, there are only 13 of us that know."

There had been several gay characters in Doctor Who before Bill Potts stepped into the blue box, (Jack Harkness, Madame Vastra and Jenny Flint - for starters) but her relationships and sexuality were the best explored than her predecessors.

During Bill's time exploring with The Doctor, she was seen dating girls and falling in love with Heather, who saves her life and whisks her away on cosmic adventures at the end of the 2017 series.

But as Pearl Mackie explained when the series started, being gay was just one small part of Bill's appeal.

"There are so many elements to Bill, there’s so much to dive into as an actor, that her sexuality is quite far down the list of things that I’ve thought about," she told Entertainment Weekly earlier this year.

"For me, I think representation is really important. You know, it’s 2017, so it’s about time for a gay main companion, really."

Martha Jones wasn't the first black person to travel in the TARDIS, but she was the first full time companion and brought cultural issues to Doctor Who storylines from 2007.

Even a robot dog had been a full-time Doctor Who companion before a person of colour.

"I never in my wildest dreams thought I'd actually become the new companion," said Freema when she was announced as David Tennant's companion, following the departure of Billie Piper, who played Rose Tyler.

Martha's character raised questions of racial equality during time travel storylines on the show, such as Elizabethan England and depression-era America.

Doctor Who companions are known for falling under the spell of Doctor Who (no matter who's playing him) but not Donna Noble. Catherine Tate's character kept David Tennant on his toes with her no-nonsense approach to time travel.

From the moment she appeared on the show, it was clear that there would be no love story between Donna and The Doctor and instead won over audiences with her sense of humour.

"Donna is much more the Doctor's equal than any of the previous assistants," said writer Russell T Davies in an interview with The Telegraph in 2008.

"She is older and she is not in love with him, and that also makes a difference."

He added that Donna brought a bit of real life to the TARDIS, following the intergalactic almost-romances with Rose and Martha.

"She is flawed. It really is like having me or you on the TARDIS," he said.