Doctor Who season 11 is packaged with a whole regeneration's worth of changes, including a completely new Doctor, showrunner, and cast of characters who will either side with or against the time-traveling alien. Within this new era, Doctor Who is bringing some of the biggest changes - with its new creative team, the first female Doctor, and the series' first writers of color behind the scenes - so it'll certainly help to be up to speed on the Doctor's new companions, acquaintances, and enemies.

In the eleventh season of Doctor Who, the Thirteenth Doctor (played by Whittaker) has fallen to Earth from her TARDIS (hence the premiere episode being titled "The Woman Who Fell to Earth," a play on The Man Who Fell to Earth starring David Bowie) following an explosive regeneration. In her new form, she meets three humans named Yasmin Khan (played by Mandip Gill), Ryan Sinclair (played by Tosin Cole), and Graham O'Brien (played by Bradley Walsh), and ultimately recruits them as her new companions. Per Doctor Who's long-running tradition (55 years, to be exact), the Doctor and her companions travel through time and space in her TARDIS (which stands for Time and Relative Dimension in Space), answering the call of individuals - humans or otherwise - in need of help.

Related: Doctor Who Season 11 Trailer Breakdown: 13 Reveals & Secrets

Story-wise, this season of Doctor Who is mostly under wraps, aside from a handful of minor details. So, given the major changes being introduced this year, a solid understanding of new characters in the show will no doubt be useful for even the most diehard Whovians.

Jodie Whittaker is The Doctor

Jodie Whittaker 13th Doctor

Leading the charge in season 11 of Doctor Who is, of course, The Doctor. Having just regenerated from her twelfth incarnation (played by Peter Capaldi), the Doctor is facing some unique challenges in her thirteenth go: she has no TARDIS, no sonic screwdriver, and no idea what her job title is. Naturally, this is common practice for the Doctor post-regeneration, and everything will eventually fall back into place - though not without some major bumps (and the occasional Bootstrap Paradox) along the way.

This is Whittaker's first season as the Doctor, and she previously worked with Chris Chibnall (Doctor Who's brand new showrunner) on the BBC series Broadchuch (which, incidentally, also starred David Tennant, who played the Tenth Doctor, David Bradley, who played the First Doctor, and Arthur Darvill, who played companion Rory Williams).

Mandip Gill is Yasmin Khan

Mandip Gill and Jodie Whittaker in Doctor Who

One of the Doctor's new companions is Yasmin Khan. A Police Constable in Hallamshire, little else is know about her ultimate role in the series, nor why the Doctor ultimately brings her aboard the TARDIS. That said, she is one of three people who are present when the Doctor falls from the sky and lands in their small town. She is played by Mandip Gill (The Good Karma Hospital).

Related: Doctor Who Theory: Thirteen MAKES Her Sonic Screwdriver

Tosin Cole is Ryan Sinclar

Tosin Cole as Ryan Sinclar in Doctor Who

The second of the Doctor's newest companions is a young man named Ryan Sinclair. In the first clip released for the new season's premiere episode, he's walking alongside Yasmin, though it's unclear whether or not the two work together. In fact, the only solid takeaway from that clip that refers to his identity is the fact that he is not a doctor. Ryan is played by Tosin Cole (Burning Sands), and this won't be the actor's first foray into mainstream sci-fi, as he also had a small role in Star Wars: The Force Awakens.

Bradley Walsh is Graham O'Brien

Bradley Walsh and Jodie Whittaker in Doctor Who poster

Rounding out the new trio of companions is Graham O'Brien, played by UK personality Bradley Walsh (Law & Order: UK, Coronation Street). Noticeably one of the oldest companions that the Doctor has ever welcomed aboard the TARDIS (not counting some extraterrestrial characters who look much younger than they actually are), Graham has a slightly mysterious background, according to an interview Walsh gave to the Metro, though his lack of clarity keeps the mystery strong. He said:

"Everything on a daily basis is brand new for my character, and out of interest for my particular character. It’s a situation. But when you find out during the show, when it comes out what he did and what he does for a living, then you’ll get it. Under no circumstances in a normal job would you understand it, it would be mind-blowing."

Walsh also appeared on the Doctor Who spinoff series, The Sarah Jane Adventures.

Sharon D. Clarke is Grace O'Brien

Tosin Cole Mandip Gil Jodie Whittaker Bradley Walsh and Sharon D Clarke in Doctor Who

One character who is very much aligned with the Doctor and her companions, but isn't an official companion herself, is Grace O'Brien - Graham's wife. Showing up in some promo material for the new season, as well as screenshots from the premiere episode, Grace will be a recurring character on the show, though it's unclear how often she'll appear. Played by Sharon D. Clarke (EastEnders, Thunderbirds Are Go!), Grace appears to be in full support of her husband running through time and space.

Related: Doctor Who: The Best (And Worst) Companions So Far

Doctor Who's Supporting Cast

Lee Mack Alan Cumming and Shaun Dooley

Season 11 of Doctor Who will feature a variety of new characters, some whose identities are still under wraps, and some who have been inadvertently outed. This currently small list of supporting actors include Alan Cumming (X2: X-Men United, Goldeneye) as King James I, who will reportedly make several appearances this season. Cumming revealed on the Homo Sapiens podcast that his character will have a strong arc in terms of his allegiance to the show's protagonists.

Two other actors who have been confirmed to appear in this season of Doctor Who include Lee Mack (Not Going Out) and Shaun Dooley (Misfits, Broadchurch), with the latter known to be appearing in season 11's second episode, which is titled, "The Ghost Monument."

More: Doctor Who Season 11: Every Update You Need To Know

Season 11 of Doctor Who will air October 7 on BBC America and BBC One.