Regardless of the format, Doctor Who is only as good as its companions. While the Doctor is a key part of the success of any series, the companions can often guide the stories and define the overall personality of the Doctor. They join him or her on most adventures, even in the books or comics.

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While the Doctor is clearly the leader of the group, that doesn't mean that his companions don't add some really key things to their adventures. In fact, there's been plenty of times the Doctor has been surprised by his companions; here's 10 times he underestimated them.

CLARA IN THE TIME STREAM

Clara was involved in the huge 50th anniversary of the show and as such was also a part of a pretty big storyline. The Doctor's past came back to haunt him during these episodes and Clara was actually there to save the day.

The impossible girl inserted herself into the Doctor's timeline, fixing many mistakes, helping him choose the right T.A.R.D.I.S. and even becoming a long term companion. The Doctor never expected she could help him so much.

BAD WOLF

Rose Tyler broke the Doctor's expectations so many times and was one of the few people he genuinely fell in love with. The heart of the T.A.R.D.I.S. is a dangerous place and shouldn't be looked at by a mere mortal.

Yet, Rose managed to stare directly at it and became the Bad Wolf, changing multiple events and handling huge amounts of power. They had to be removed eventually but the moment certainly shocked the Doctor and demonstrated her strength.

DOCTOR DONNA

Donna Noble was often underestimated by the twelfth Doctor, ever since he first met her. He absolutely didn't predict that they would reunite and actually travel together. She also surprised him when she took on the mind of a time lord.

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Becoming the Doctor Donna, she completely blew him away with the amount of time she managed to hold the knowledge of the universe in her head. Unfortunately, the only way to solve this without killing her was to completely wipe her mind.

BILL'S SURVIVAL

Bill was one of the more unexpected companions to the Doctor. She was far more intelligent compared to many of the other companions and immediately threw herself into danger. She's a great character and it's a shame she left the show so quickly.

Tragically the Cybermen actually converted Bill, but that didn't stop her from turning on her creators and getting revenge. What was more shocking was her spirit was saved and she is now seeing the universe alongside her lover.

CRAIG OWENS FIGHT BACK

Craig Owens wasn't in the show much, but each time he appeared he genuinely shocked the twelfth Doctor and produced some of his best episodes. The character was also converted into a Cyberman, much like Bill after him.

However, Craig managed to completely fight back against this conversation and deletion, bringing back his emotions by remembering his son. It was a moment that felt heartwarming but also showed the Doctor that a father's love shouldn't be underestimated.

AMY'S CHOICE

Amy Pond isn't just the girl who waited. Although to be fair she once waited such a long time that the Doctor was impressed that she even managed to survive in such a hostile environment. Amy is a survivor though, through and through.

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During an episode where the Dream Lord took over, Amy was put in such a difficult situation and had to make a choice between what was real and which world was fantasy. She shocked the Doctor with her will power and her ultimate decision.

JACK'S RESURRECTION

Captain Jack is an impressive individual and went down fighting the Daleks. Due to Rose's Bad Wolf powers however, he was revived. This wasn't something the Doctor could account for though and he left him behind without realizing.

The Doctor encountered Jack many times since and each time he is shocked. Whether it's the reveal that he's the face of boe or perhaps the fact that Jack managed to hold onto the blue box through time, the Doctor is learning not to underestimate him.

MARTHA'S RESISTANCE

Martha Jones stands in the TARDIS in Doctor Who.

The Master once took over the Earth with lethal metal drones. As strange as that sounds Martha managed to launch a small resistance and started to revolt. Her tactics and recruitment strategy were incredibly well thought out.

She was so impressive that she made a real difference during the overall fight. Her actions eventually cost the Master his plan and the Doctor was severely shocked at how well she had performed during this difficult time. She's one of the best companions on this list.

PARALLEL MICKEY

Mickey was often perceived to be a bit useless and yet on the parallel Earth, he really excelled, with his doppelganger. He did so well fighting off the Cybermen that he eventually chose to stay, completely shocking the Doctor.

There was a level of respect there that hadn't been around before and the Doctor was impressed with how Mickey had handled himself. Each time they came into contact since the Doctor knew not to underestimate this fighter.

RORY THE CENTURION

The girl who waited has the perfect husband as he became the boy who also waited. Rory the Centurion waited years and years guarding the Pandorica across centuries until it ultimately opened with Amy Pond re-emerging into the world.

This was one of the biggest sacrifices that any companion has ever had to make and Rory's life would never be the same after that. He would always be a selfless hero in the eyes of Amy and the Doctor, which is why his eventual weeping angel demise was so sad.

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