This question has been asked before, but it only included the three most recent mainstream Doctors; it didn't encompass the whole classic series. We've also brought something similar up for non-mainstream Doctors like the Valeyard, but this is focusing on mainstream, protagonistic Doctors. Can you give me a list in order of who you think are the Darkest Doctors you're familiar with? That would be awesome! And if you think the War Doctor shouldn't count as a mainstream Doctor, you don't need to include him.

Is it the First Doctor?

Is it the Second Doctor?

Is it the Third Doctor?

Is it the Fourth Doctor?

Is it the Fifth Doctor?

Is it the Sixth Doctor?

Is it the Seventh Doctor?

Is it the Eighth Doctor?

Is it the War Doctor?

Is it the Ninth Doctor?

Is it the Tenth Doctor?

Is it the Eleventh Doctor?

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1. The War Doctor
2. The 9th Doctor (tecnically the war doctor was supposed to be Christopher E, or the ninth doctor, but He didn't want to appear in the episode so they cast a new doctor)
3. Doctor #7. I haven't seen much of the old series but from what I've gathered, #7 is the darkest
4. Since the above is technically 2, Tennant (best doctor!)

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The war doctor or 9

For darkest, I'd have to go with Six or Seven.

The Sixth Doctor had some dark moments early on. In particular right after his regeneration he briefly goes delusional and attacks his companion, Peri. Later, in a story Vengeance on Varos, he's straight up killing a guy and even delivering a 'bond one liner' when he does it.

Seventh Doctor had his dark moments. Perhaps the most infamous is deliberately insulting and berating his companion, Ace, because her faith in him was actually hindering stopping the bad guy, or deliberately taking her to a place that had traumatized her in her youth in the name of helping her get past that trauma.

Recently re-watched the Ninth Doctor episode Dalek, which was definitely a dark moment for the Ninth as he went ballistic regarding the Dalek of the episode.

The darkest moment for Ten would probably be the whole "Time Lord Victorious" thing, but I think that's more a moment of weakness. But I haven't seen the full ep so maybe I'm missing something.

Seventh, without a doubt. I might have limited knowledge of the classics, but I know this much for a fact. He is both the darkest realization, and at the same time the most out of reach and wibbly wobbly of the bunch. Which is what I personally find iconic for the Doctor.
It's what the scriptwriters were gunning for, most likely. He shined and underlined all that the Doctor was supposed to represent. But then the series ended, and the Americans came up with the eight regeneration. That's how it went, right?
I didn't even bother with going through the whole episode. Not after I saw what they've done with the Master. <shudders and writhes, holding back barfs>

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Thanks for your own responses!

I'll give my own list:

5. The Second Doctor:
True he was a goofball; in fact, that's exactly why his darker moments seen in The Moonbase, Tomb of the Cybermen, and that time he imploded a galaxy or tricked enemies into destroying themselves, made all the impact. Not as dark as often given credit for, since most of the time what he did seemed necessary to stop intergalactic threats, but it was remarkable to see the change!

4. The Sixth Doctor:
He usually wasn't as dark as shown in The Twin Dilemma, but he still had some scary episodes, and with them, some rather scary moments, though except for The Twin Disaster Dilemma, most of this would be interpreted as him taking on the right attitude for his situations. He would kill, he would get angry, and certainly more so than the Second, but if you were in his olive-green shoes, you probably would too.

3. The Tenth Doctor:
This guy crossed the line a little more than the Second and Sixth usually did. Like the time he burned the Racnoss Queen's children, but some would argue that as necessary, so I'll think of better examples. How about how he treated the Family of Blood? Or that time he declared himself "The Time Lord Victorious"? Sure killing should have been a decent answer, but he did worse than kill, the Family were eternally damned, basically, and he underwent a particularly dark God complex.

2. The Seventh Doctor:
If you don't believe me, just watch these:

1. The Ninth Doctor
In almost any other group, this would have gotten a lot of disagreement. I probably don't need to explain to you guys, but I shall. The Ninth Doctor would have wiped out the human race to stop the Daleks, and he tortured a Dalek to get even with it for all its crimes. What's more is that this incarnation, while probably not the same, is still remarkably similar to the War Doctor, to the point where they are almost the same (but not quite); in fact, until the Eleventh Doctor's run, it was implied that the Ninth Doctor was the one who destroyed Gallifrey, not the Eighth like many believe. Of course that's been retconned to have Gallifrey spared and to include the War Doctor.

Honorable mentions

The First Doctor
The thing is, a lot of fans watch the scrapped pilot that was quite stupidly included before anything else on the DVD release of his earliest adventures and then give up on him on the premise that he was "a d*ck" and declare him too dark and unlikable to be watched. The scrapped pilot is non-canon, and should never have been included except on the bonus features, not as an alternate opening to An Unearthly Child. If you ignore the original pilot, you realize that the First Doctor isn't a bad guy, just over-protective of himself and Susan, and by Marco Polo, becomes over-protective of Ian and Barbara too. However, he is so over-protective that he will leave others for dead to save his companions (a trait almost unique this this incarnation), much to their protest, and he is far darker than still that in the pilot, so he's worth mentioning.

The Fourth Doctor
Many would include the Third Doctor instead, but he was probably the least dark Doctor; he was just in a series that was darker than the stuff in the 60s: NEVER confuse a dark Doctor for a dark series! The Fourth Doctor, however, not only had a series that was darker than often credited for, he was sometimes a brooding character to match. He occasionally killed, which he needed to do, if you think about it, but he was more than willing to threaten Davros with death, by means of a sort of torture. Now he probably needed to do that too, we all know how easy it is to reason with Davros without getting cruel, but that's seriously pretty damn dark!

The Eleventh Doctor
Often cited as the darkest Doctor, this is a serious case of confusing a dark series for a dark Doctor. However, like the Second and Fourth Doctors he's based on, this darkness was often brought out of him by being surrounded by extremely ruthless enemies, like the Silence. However, as implied, he still had his dark moments, such as when baby Melody was stolen, and that episode in which he was recovering from the loss of Amy and Rory. Most of the time he still seemed kind of benign even when being Machiavellian, but he's still an honorable mention for things like I mentioned.

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It occurs to me, reading this, that the Doctor's darkest moments truly come about when his anger is roused. He may do some ruthless things, but even then he's never actively malicious about it unless angered by something.

The Tenth Doctor and the Family of Blood, Eleven work the Kovarian sect or the old man in Dinosaurs on a Spaceship Nine with the Dalek, Two with the Ice Warriors in Seeds of Death. This is more common in the new era, as the above suggests, since we now have a Doctor scarred by the Time War. That and I'm not intimately familiar enough with classic era to name times the Doctor was angry.

Perhaps Seven is the exception. His darkness stems from being even more ruthless than average when sound what he has to do.

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Yay we have the same top 3!