For over 55 years, Doctor Who has entertained audiences the world over. Every episode follows the adventures of a mad man (or woman) in a police call box that just so happens to be a time traveling space ship, otherwise known as the TARDIS. That mad time traveler is, of course, known as the Doctor, and there's seldom an adventure during which this beloved alien isn't joined by one of his or her many friends, best known as companions.

There have been over a dozen iterations of the Doctor character so far, but only a handful of them can be considered as part of the true new Who canon, which was launched with the revival of the series in 2005. Since the series was launched once again with Christopher Eccleston's Ninth Doctor, a dozen main companions have come and gone, some of whom were much better than the others. Here's our official ranking of the best and worst of them all.

BILL POTTS

Pearl Mackie as Bill Potts in Doctor Who

To be fair, Bill Potts did add a lot of good to the series: she gave the series its first female lead of color since Martha Jones, nearly a decade before, and she introduced a prominent form of LGBTQ representation to a series that had long been hesitant to stray away from its comfort zone.

But beyond giving the series some much needed diversity, it's also clear that Doctor Who never really figured out what to do with her character. Bill's bond with the Doctor never gelled in any meaningful or emotional way, and the ending to her storyline - being written out by becoming a water-like creature in order to explore the universe with her girlfriend - is hardly the best written ending any of the series' companions has received.

AMY POND

Amy Pond with Melody in Doctor Who

When Amy Pond was first introduced as little Amelia Pond in the fifth season's first episode, there seemed like there could be great promise for the character. Having a child as the Doctor's prospective companion would have been something truly new and unique, and for the half episode the two spent together, as the Eleventh Doctor adjusted to life after regenerating, it was comedy gold.

And then, Amelia grew up, and became Amy - an overly opinionated troublemaker who spent the vast majority of her scenes screaming if she didn't get her way. Briefly interesting storylines about her role in the universe, particularly the sixth season episode "The Girl Who Waited," were nevertheless undercut with the reveals that she essentially only ever existed to give birth to River Song. By the time her character left the series, she had long over stayed her welcome.

YASMIN KHAN

Doctor Who Yaz

Of the three new companions - or, "team, gang, fam" members - introduced along with Jodie Whittaker's Thirteenth Doctor, Yasmin Khan is perhaps the least satisfying and enjoyable to date. Although she has received the most attention of the trio, Yaz's character still somehow feels as though she has seldom been explored or developed in any way.

Her character has allowed the series to explore new aspects of the universe, particularly in terms of true events in history the series has never explored before. But beyond learning about her family history, and her current dynamics with her family, it still feels like we don't know anything about her. Her relationship with the Doctor, and with her fellow companions, is, so far, unremarkable.

MICKEY SMITH

Mickey Smith may not have been one of the world's best boyfriends, at least as far as Doctor Who significant others go, but even that judgment that fans are so quick to make is entirely made in comparison with the belief that the Doctor could ever be an ideal significant other. Even if Mickey wasn't the right guy for Rose, he was still a devoted partner and companion in his own right.

He undergoes quite the transformation over the course of his few seasons on the series as well. While girlfriend Rose is fearless and willing to join up for the adventures from the very beginning, Mickey is initially much more reserved and afraid; but soon enough, he's along for the ride, too, helping to save the day - and the universe - on more than one occasion.

NARDOLE

Matt Lucas as Nardole in Doctor Who

It's not every day that a Doctor Who companion exists primarily for comedic effect. It's also not every day that such a companion exists, and does so in an enjoyable way. But Matt Lucas's Nardole, the Twelfth Doctor's other companion during his final season, offers the otherwise difficult season some of its few moments of levity.

Nardole also has the rare distinction of being the first of the new Who companions to be an alien. Hailing from the planet Mendorax Dellora, Nardole is a member of a species from the 54th century, totally unfamiliar with earthly customs and behaviors, and offering seemingly endless moments of hilarity as a result of it in his interactions with Bill and the Doctor both.

GRAHAM O'BRIEN

As one of the trio of new companions introduced in the series' eleventh season, Graham O'Brien has undergone quite his fair share of journeys already. When the season began, Graham was Ryan's new step-grandfather, happily married to Grace and struggling to get close to the grandson he had acquired through marriage. By the end of the premiere, however, he found himself a widower, setting off on journeys through time and space the likes of which he could never have imagined.

Along the way, Graham became not only a true grandfather to Ryan, but a father, as well. Their relationship proved to be one of the real standouts of the season, particularly as Graham took on the responsibility of going toe to toe with both the Doctor and Ryan's own absentee father. Graham provides the new Team TARDIS with a source of equal parts humor and reason.

MARTHA JONES

Martha Jones looking confused in Doctor Who

Martha Jones had the unenviable task of following in the footsteps of one of the most beloved companions of them all, Rose Tyler. While some were unwilling to give the new girl a chance, those who did were rewarded with the introduction of a brilliant, brave, and totally badass medical student who became as invaluable a support to the Doctor as Rose ever was - if not more so.

Martha remains one of the series' most fiercely independent and inspiring companions to date. She knows her limits, and isn't afraid to leave her role as the Doctor's companion when the time comes - and it's worth noting that this alone is something that few companions have been able to do. Further, in her absence from the Doctor's service, she goes on to become a hero in her own right, working with UNIT and Torchwood to protect the universe even when no longer a companion.

RYAN SINCLAIR

An image of Ryan eating his dinner in a diner in Doctor Who

Arguably the best companion to come from the Thirteenth Doctor's tenure so far is Tosin Cole's Ryan Sinclair. In addition to being one of the youngest companion so far at only nineteen years old, Ryan has had some of the strongest development of any of the series' leads to date. When the series begins, Ryan is struggling with the loss of his Nan, as well as his dyspraxia, a disability that affects his motor skills and makes him less sure of his actions and, at first, afraid of taking part in big adventures.

But by the end of the season, and, in particular, the New Year's Day special, Ryan has proven himself to be the very bravest and one of the best of them all. His emotional journey in his relationships with his grandfather, Graham, and his absentee father, Aaron, also provided the shaky eleventh season with some of its most important, most emotional moments.

ROSE TYLER

Rose Tyler from Doctor Who looking off camera.

It's not a surprise when someone reports that Billie Piper's Rose Tyler is their favorite companion. As the introductory character for the entire revival series, it was Rose who made the entire world of new Who possible, in a way, and it was her relationship with both the Ninth and Tenth Doctors that showed a new generation of viewers what a Doctor and companion relationship could really be like.

Of course, the relationship between Rose and David Tennant's Tenth Doctor would go on to become a storyline both beloved and loathed by fans in equal measure. And though Rose certainly reared her head one too many times over the years in various specials, her contribution to early parts of the series as Bad Wolf made for some of new Who's strongest storytelling.

CLARA OSWALD

Souffle Girl. Oswin. The Impossible Girl. The girl who was born to save the Doctor. Few characters have boasted as many monikers as Jenna Coleman's Clara Oswald, an unsuspecting teacher at the famed Coal Hill School who gets swept up in the Doctor's many intergalactic adventures, and becomes all too eager to go along for the ride.

In the seventh season, it's revealed that Clara's involvement in the Doctor's entire life has perhaps been more monumental than any other companion so far, with her bond going all the way back to the First Doctor's escape from Gallifrey. It was a version of Clara, after all, that encouraged the Doctor to choose the TARDIS he did. Over time, the series embarks on a truly fascinating analysis of what it means for someone human to want to become the Doctor, with Clara's thrill seeking personality perfectly suited for some of the series' most philosophical adventures.

RORY WILLIAMS

Rory Williams holding onto a sword while wearing a red cape in Doctor Who

When Rory Williams was first introduced in the first episode of the series' fifth season, it would have been difficult to anticipate just how significant a character the future lone centurion would become. Beyond the role he played in his relationship with Amy, which would of course lead to the birth of time traveler River Song, Rory's character undergoes a true heroic journey.

After disappearing from history through his death in the fifth season, Rory is written back into existence as the lone centurion during the Doctor's adventures with the Pandorica. Waiting 2,000 years to return to Amy and the Doctor, Rory's legacy is cemented as "the boy who waited." Watching the adorably nerdy nurse go on to become one of history's greatest heroes made for quite the enjoyable viewing experience.

DONNA NOBLE

Donna in Doctor Who

Few companions have ever meant more to Doctor Who than Catherine Tate's Donna Noble. As one of the few companions in the new Who run to not have any romantic entanglement with the Doctor, or at least any pretensions of one, Donna has the distinct pleasure of being known simply as one of the Doctor's very best friends. Matching David Tennant's wit measure for measure, Tate's Donna was a true spitfire personality, leading to some of the series' most hilarious moments.

But Donna also received one of the most unfair endings of them all, as well, having her memories of her time with the Doctor totally stripped from her mind in a truly devastating moment. For all the highs and lows that came with her character, there's no denying that Donna was simply the best of the best.

NEXT: Doctor Who Season 11: Every Episode & Spoiler You Need to Know