Doctor Who pits a mad man in a box and all his companions against aliens, monsters, demons and everything else the universe has to throw at them. Having a "powerful" way with words just comes naturally.
The new series shows that the Doctor can do these indirectly and evil will retreat.
"I'm the Doctor, and you're in the biggest library in the universe. Look me up."
Similarly, from the Eleventh Doctor's premiere...
The Doctor: One more question. Just one. Is this world protected? (As one of the Monsters of the Week looks at records of various other MotW that have attacked Earth, ever.) 'Cause you lot aren't the first to come here. Oh, there have been so many. What you have to ask yourselves is: What happened to them? (The MotW get a montage of all Doctors from William Hartnell to David Tennant with Matt Smith emerging from the image of the last Doctor) Hello. I'm the Doctor. Basically... run.
In The Big Bang, River notes that she has the ability to kill a weakened Dalek, and the Dalek points out that records indicate the Doctor's companions always show mercy in such situations. "I'm River Song. Check your records again." The Dalek stops, then begs for mercy.
The Doctor: No! 'Cause this is what I'm going to do: I'm going to rescue her! I'm going to save Rose Tyler from the middle of the Dalek fleet! And then I'm going to save the Earth! And then, just to finish off, I'm going to wipe every last stinking Dalek out of the sky! Dalek 1:But you have no weapons! No defenses! No plan! The Doctor:Yeah! And doesn't that scare you to death? Rose? Rose: Yes, Doctor? The Doctor: I'm coming to get you.
Rose gets one in The Parting of the Ways when she absorbs the time vortex and returns to rescue the Doctor:
Rose: I looked into the TARDIS and the TARDIS looked into me. I am the Bad Wolf. I create myself. I take the words... I scatter them, in time and space. A message, to lead myself here. I want you safe, my Doctor. Protected from the false god. Dalek Emperor:You cannot hurt me, I am immortal. Rose: You are tiny. I can see the whole of time and space, every single atom of your existence. And I divide them. Everything must come to dust. All things, everything dies. The Time War ends.
Older Doctor Who series also had these, usually delivered by Tom Baker. "I am a Time Lord. I am not a human being. I walk in eternity."
"Do you know what they call me in the ancient legends of the Dalek homeworld? 'The Oncoming Storm'. You may have removed all your emotions, but I bet that deep down in your DNA there's one spark left, and that's fear."
Later subverted when Rose is captured by some clockwork robots, and the Doctor is elsewhere. She tries (unsuccessfully) to basically redo his "Oncoming Storm" boast by proxy, but gets drowned out by a very drunk Doctor bursting into the scene just in time.
Rose: Oh, look what the cat dragged in. The Oncoming Storm. Doctor: You sound just like your mother!
Then she pulls it off right in Doomsday. After the Daleks and Cybermen verbally joust (read below), the Daleks wonder why one man in the picture makes Rose's heart race. When she finally admits it's the Doctor, all the Daleks in the room roll back a bit: their way of taking a very nervous step backward.
Rose: Five million Cybermen, easy. One Doctor? Now you're scared.
Of course, Rose herself gets to make a particularly effective boast (though it does pale in comparison to the Doctor's, it still gets points for being intended as a Defiant to the End boast):
Rose: I met the Emperor. And I took the Time Vortex and poured it into his head and turned him into dust. D'you get that? The God of all Daleks and I destroyed him. HAH!
"Well, you need to get yourself a better dictionary. When you do, look up 'genocide.' You'll find a little picture of me there, and the caption'll read 'Over my dead body.'"
Of course, you'll also just find a picture of him. Mostly against the Daleks though.
The Beast: "This is the Darkness. This is my domain, you little things that live in the light, clinging to your feeble suns... which die. Only the Darkness remains."
And of course nearly everything the Daleks say for the Villain to Hero variety. Or in the case of the episode "Doomsday", Villain to Villain:
Cyber Leader: Daleks, be warned. You have declared war upon the Cybermen. Dalek Sec: This is not war — THIS IS PEST CONTROL! Cyber Leader: We have five million Cybermen. How many are you? Dalek Sec: Four. Cyber Leader: You would destroy the Cybermen with four Daleks? Dalek Sec: WE WOULD DESTROY THE CYBERMEN WITH ONE DALEK! You are superior in only one respect. Cyber Leader: What is that? Dalek Sec: You are better at dying.
In this case, Dalek Sec is not only boasting, but making an objective statement of fact. The odds really were that one-sided. In spite of the Cyber Leader calling in reinforcements, the Daleks later pretty much gunned them down with impunity.
In "Dalek", a lowly soldier Dalek has been trapped and tortured on Earth after escaping the Time War, and believes that it is the last of its kind. After tricking Rose into freeing it, killing its torturer, disabling its prison and draining half of American of power, it lets out a single cry.
Dalek: THE DALEKS SURVIVE IN ME!
From Voyage of the Damned: "I'm the Doctor. I'm a Time Lord. I'm from the planet Gallifrey in the constellation Kasterberous. I'm 903 years old, and I'm the man who's going to save your lives, and all six billion on the planet below. You got a problem with that?"
Parodied in The Day of the Doctor, where the Doctor delivers almost exactly that speech...to a rabbit.
A quieter variation took place in Planet of the Dead, where the Doctor calmed down the passengers of a bus trapped on a distant planet after their bus-driver died trying to pass through the wormhole, by reminding them of their lives back on Earth. This time around he was more able to keep his promise: "That planet out there, with three suns, wormhole and alien sand, that planet is nothing—you hear me, nothing—compared to all those things waiting for you. Food, home, people—hold on to that. 'Cause we're gonna get there. I promise. I'm gonna get you home."
The Eighth Doctor in the audio adventure "Phobos": "Was that supposed to frighten me? I've seen entire species destroyed, civilisations left in ruins. I've witnessed solar systems vanish in the twinkling of an eye. I've seen things that would freeze your blood. So don't threaten me. Don't ever threaten me."
Also from the Eighth Doctor, in the Doctor Who New Adventures novel The Dying Days: "I am the man that gives monsters nightmares. The Daleks call me the Bringer of Darkness. I am the Eighth Man Bound. I am the Champion of Life and Time. I'm the guy with two hearts. I make History better. I am the Doctor."
Davros: We shall become all— The Doctor: -Powerful! Crush the lesser races! Conquer the galaxy! Unimaginable Power! UNLIMITED RICE PUDDING! Et cetera! Et cetera!
And (goodness, there's a lot, aren't there?) from the audio "Death Comes to Time", a commander gives orders to his men about a battle they all know they're going to lose.
"Resist the Canisians. Breathe harder to starve them of air, and as they kill you bleed on their boots. Offer them no compliance, no words, no recognition of existence."
And in "The Family of Blood", Tim Latimer makes a badass boast on behalf of the Doctor: 'I've seen him. He's like fire and ice and rage. He's like the night, and the storm in the heart of the sun. He's ancient and forever... He burns at the center of time and he can see the turn of the universe... And... he's wonderful.'
"The Time of Angels" have another, with his response to the Weeping Angels taunting him.
The Doctor: There's one thing you never put in a trap if you're smart. If you value your continued existence, if you have any plans about seeing tomorrow there's one thing you never, ever put in a trap. Angel Bob: What's that, sir? Doctor: Me.
From "The Pandorica Opens", we have this speech, delivered to a swarm of hostile spaceships containing every single one of the Doctor's many enemies above Stonehenge.
Doctor: Hello Stonehenge! Who takes the Pandorica, takes the universe! But, bad news everyone, 'cause guess who! HAH! You lot, you're all whizzing about, it's very distracting. Could you all stay still for a moment, because I! AM! TALKING! Now the question of the hour is who's got the Pandorica. Answer: I do. Next question: who's coming to take it from me? Come onnnnnn! Look at me, no plan, no backup, no weapons worth a damn. Oh, and something else: I don't have anything. To. Lose. So! If you're sitting up there in your silly little spaceships with all your silly little guns, and you've got any plans on taking the Pandorica, tonight, just remember who's standing in your way. Remember every black day I ever stopped you. And then, AND THEN, do the smart thing. Let someone else try first. [cue shot of spaceships flying away]
What makes this Badass Boast pure Doctor? He opens his speech by dropping the microphone and then apologizing.
Also from "The Pandorica Opens" the Doctor makes a completely unintentional Baddass Boast, unaware that the creature he's describing is himself (made all the better when you recall all the times he's boasted about the things that fear him):
Doctor: There was a goblin. Or a trickster, or a warrior. A nameless, terrible thing, soaked in the blood of a billion galaxies. The most feared being in all the cosmos. Nothing could stop it, or hold it, or reason with it – one day it would just drop out of the sky and tear down your world.
Undercut when it's revealed that they were just pretending to be scared to lull him into a false sense of security, though the fact that they felt they still had to do this to convince the Doctor does speak volumes.
However, the Doctor's timing for these is sometimes less than stellar. In addition to a couple mentioned earlier where he failed to make good on them, there's "The Lodger," where he hears somebody mention annihilating their enemies and immediately launches into one of his Oncoming Storm speeches about how he won't allow annihilation on his watch, only to belatedly realize they were talking about football.
From "The Doctor's Wife":
House: Fear me, Doctor. I've killed hundreds of Time Lords. The Doctor: Fear me. I've killed all of them.
In the Series 6 episode "A Good Man Goes to War," Matt Smith's excellent delivery of the 11th Doctor's retort to the assumption that he is a good man and good men won't do anything bad when angry makes the statement far more threatening than it would be otherwise.
Madam Kovarian: The anger of a good man is not a problem. Good men have too many rules. The Doctor: Good men don't need rules. Today is not the day to find out why I have so many.
Earlier in this episode, Amy got to Badass Boast on behalf of her husband Rory:
Amy Pond: [to her baby] I wish I could tell you that you'll be loved, that you'll be safe, and cared for, and protected, but this isn't the time for lies. What you are going to be, Melody, is very, very brave. But not as brave as they all have to be, because there's somebody coming. I don't know where he is, or what he's doing, but trust me: he's on his way. There's a man who's never going to let us down, and not even an army can get in the way. He's the last of his kind. He looks young, but he's lived for hundreds and hundreds of years. And wherever they take you, Melody, however scared you are, I promise you, you will never be alone, because this man is your father. He has a name, but the people of our world know him better... as The Last Centurion.
Made even better because until the last two words, every viewer thinks she's talking about the Doctor, even when she mentions the "father" bit. And the Doctor does have a name. It's just that nobody knows it.
Leela has one in "The Sunmakers", when she's being held hostage to force the Doctor to do something. Someone tells her that she'll die if he doesn't come back. "Then I die." (Pulls out her knife.) "But before I do, I'll see this rat's nest knee deep in your blood. That is a promised thing." (One of the hostage takers says that if she has to be killed, he won't be the first on his feet.)
Leela gets another good one in The Talons Of Weng Chiang. She's about to be killed in a particularly painful manner by Magnus Greel (for the purpose of prolonging his life by a means that is rapidly losing effectiveness), and this only makes her angry:
"When we are both in the Great Hereafter, I will hunt you down, Bent-Face! And put you through my agonies a thousand times!"
I cross the void beyond the mind The empty space that circles time I see where others stumble blind To seek a truth they'll never find Eternal wisdom is my guide I am the Doctor!
Through cosmic wastes the TARDIS flies To taste the secret source of life A presence science can't deny Exists, within, outside, behind The latitude of human minds I am the Doctor!
My voyage dissects the course of time "Who knows?" you say, but are you right? Who journeys deep to find the light That glows so darkly in the night? Toward that point I guide my flight
As fingers move to end mankind Metallic teeth begin to grind With sword of truth I turn and fight The satanic powers of the night
Is your faith before your mind?
From "The Rings of Akhaten," to a so-called god which feeds off of psychic imprints:
The Doctor: I walked away from the Last Great Time War. I marked the passing of the Time Lords. I saw the birth of the universe, and watched as time ran out, moment by moment, until nothing remained. No time. No space. Just me. I've walked in universes where the laws of physics were devised by the mind of a madman. I've watched universes freeze and creations burn. I have seen things you wouldn't believe. I have lost things you'll never understand. And I know things. Secrets that must never be told. Knowledge that must never be spoken. Knowledge that will make parasite gods blaze. So come on then! Take it! Take it all, baby! Have it! You have it all!
Given that the Doctor later chants "home again, home again, jiggerty-jig", the Blade Runner reference was probably deliberate.
Kate:(to the Zygon who is impersonating her) Somewhere in your memory is a man called Brigadier Alistair Gordon Lethbridge-Stewart. I'm his daughter. ( Zygon!Kate's eyes widen in fear.)
Perhaps the most magnificent example occurs in the 50th anniversary special, when the War Doctor, Tenth and Eleventh Doctors call the War Council of Gallifrey and assure them that they'll do everything they can to save the planet and its commoners, without so much as firing a shot. While the members of the council admire their bravery and resolve, they question the technical feasibility of the idea, and especially the reasoning of the Doctors. Cue the following lines from the Tenth and Eleventh Doctor:
Aukon: You will all serve the Great One, Doctor, one way or another. If you do not join us you will feed him with your blood. Doctor: No. There is a third choice. Aukon: What is that? Doctor: I can destroy the Great One.
In "The Impossible Astronaut," The Eleventh Doctor gets angry when his companions are hiding something from him, and he calmly warns them, "Don't play games with me. Don't ever, ever think you're capable of that."