When you’re travelling through all of time and space, you tend to fall in situations where you need to make some hard choices. The Doctor and their companions have faced such moments aplenty, and there have been many relatively awful consequences from these decisions. Also, there have been in-universe decisions that the characters regretted later on.
Since there have been more than two dozen main characters on Doctor Who, we’ll be giving more weight to “NuWho” in this list (characters who appeared in fewer episodes, or weren't the "main" companions haven't been included), as the current fanbase feels closer to them, with the “worst” criteria comprising of the attempted actions the characters wanted to go through with that didn’t sit well with fans, and the things they actually did which still leaves us feeling sour.
10 Donna Noble: Turn Down The Doctor's Invitation
Donna was certainly the best friend the Doctor sorely needed after having a companion that was madly in love with him, but this partnership only came about a year after their initial meeting. Donna originally turned the Doctor’s invite down, citing his dangerous lifestyle one she didn’t want.
We all know what followed afterward, though, as Donna deeply regretted her decision. She spent all her days trying to locate the Doctor once more, which led to her ruining her day-to-day life. Who knows, maybe Donna could have avoided her ultimate fate had she joined the Doctor sooner.
9 Sarah Jane Smith: Pressure The Doctor To Commit Genocide
The Fourth Doctor once found himself in the position of making the ultimate decision, where just by connecting two wires he could have killed all of the Dalek population. Sarah Jane didn’t help matters, though, as she egged the Doctor on to go through with it despite his trepidation to do so.
Even though the Daleks are inherently evil, Sarah Jane’s intentions were appalling, seeing as it would have made a murderer out of the Doctor. And it’s not like Sarah was the one pulling the trigger either; her conscience would’ve been unscathed. Had the roles been reversed, we’re sure Sarah would have been just as reluctant as the Doctor to kill intelligent lifeforms.
8 The Master: Turn Bill Into A Cyberman
Even though the Master kills like it’s part of their everyday mantra, they took it to the worst levels by converting Bill Potts into a Cyberman. In fact, the Master pretended to be Bill’s friend for ten years just so he could see the Doctor’s face when he turned his friend into a machine.
Making things worse is the fact that the Doctor persuaded Bill to come along with him for this adventure, which meant he was the one who had to live with the guilt of Bill losing her humanity. As for the Master, we don’t see how any redemption can be brought after this act.
7 Bill Potts: Abandoning The Doctor's Body
Sure, Bill deserved all the happiness in the world after suffering for ten years and becoming a Cyberman, but that still doesn’t make it okay that she left the Doctor’s body in the TARDIS without confirming if he was dead or not.
The Doctor did wake up as soon as Bill left, which means Bill could have stuck around for longer than the couple minutes she did. Since she now had the power of the sentient oil (meaning she could travel anywhere within a flash), Bill could have taken the Doctor’s body somewhere to seek help in reviving him instead of bailing the first chance she got.
6 River Song: Collapsing Time
River was head over heels in love with the Doctor, to the point where she was willing to let all of time collapse because she didn’t want to kill as was required by the laws of time. When she didn’t go through with it, all of history came together and the universe’s time coursed simultaneously.
This meant that people who were supposed to have died thousands of years ago were now in the present, or rather there was no more present, past, or future, as all these were happening together. River knew the dangers before she made her decision, and all of time and space suffered for it.
5 Clara Oswald: Be Part Of The Hybrid
Clara and Doctor’s relationship was more of a love story than a friendship, with one of the Twelfth Doctor’s catchphrases being Clara’s name itself, but they were always doomed to fail.
It was because of Clara’s reckless antics that led to the Doctor becoming reckless himself. They would travel time looking to help people, but their carelessness resulted in more bad than good as seen in the case of Ashildr, whom they condemned to an eternal life of grief by making her immortal. The Hybrid (as Clara and Doctor were in tandem) was even foretold to spell the end of the universe, all because Clara was starting to bring out the worst in the Doctor and herself.
4 Amy Pond: Attempt To Be Unfaithful To Rory
Before Karen Gillan was playing a character who will potentially travel with Thor in the MCU, she was the companion of the Doctor. In her first season, Amy displayed some definite attraction to the Eleventh Doctor, but we were all appalled when she tried to get physical with him.
This was at a time when she was supposed to be getting married to Rory the very next morning! Had the Doctor not been a good guy, then Amy would have gladly been unfaithful to Rory - the same man who would later spend 2,000 years guarding her body. Amy’s attempted unfaithfulness is still a sour blip on the history of an otherwise great companion.
3 Martha Jones: Pined After The Doctor
Love sure is a wonderful feeling, but there comes a point when you need to realize that the person you’re in love with doesn’t love you back. Unfortunately, while Martha Jones was responsible for saving the world in Series 3, she doesn’t get the same recognition as the other companions because her characterization was stuck on being in love with the Doctor.
This does count as something that is “worst”, seeing as Martha came to have no respect for herself for needlessly pining for the Doctor, which sparked a case of identity crisis in her. She saved the world, but couldn’t save herself from permanent embarrassment.
2 Rose Tyler: Willing To Let Universes Die
Yes, Rose is a fierce character within the show’s canon, but that’s no excuse to want two universes to die. When the Doctor came to the alternate universe Rose was stuck in to say goodbye, Rose wanted him to take a chance and be with her in full.
The Doctor explained that both universes could collapse if he did so, but this only prompted a nonchalant “So?” from Rose. We get that she was in love with him, but for her to suggest he go through with killing all of life just because she wanted a boyfriend was the worst thing she could have said.
1 The Doctor: Leaving Jark Harkness Stranded
Seriously, out of all the bad decisions the Doctor made, this is one that still grinds the fans’ gears. The Doctor saw that Jack had been resurrected by the Bad Wolf, but deliberately left him in the far future because Jack’s immortality now made him an anomaly, something the Doctor was repulsed by.
However, this was no excuse to let the poor guy suffer, as Jack mistakenly traveled over a century before he should’ve in the past to reconnect with the Doctor, and had to endure a lifetime of pain and emotional turmoil because the Doctor couldn’t care less about him anymore.