Captain Kirk tells Spock that he doubts King Solomon would have approved of the Vulcan's manner of determining who was Kirk and who was Garth. The two of them, and Dr. McCoy, would meet Solomon (an immortal human who was born Akharin and was then living as Flint) shortly afterwards in "Requiem for Methuselah".

Garth's torture chair is a re-use in the neural neutralizer chair from "Dagger of the Mind".

According to Leonard Nimoy's memoir I Am Not Spock, he objected to the fact the plot of this episode recycled many elements from the first season episode "Dagger of the Mind."

Marta: There's nothing the matter with me! Can't you see just by looking at me ? Can't you tell by listening?
Spock: She sounds rational enough, Captain.
Marta: I am rational.

Kirk: Garth, do you have to make him suffer like that?
Garth of Izar: You will address me by my proper title, Kirk.
Kirk: I'm sorry. I should've said Captain Garth.
Garth of Izar: I am Lord Garth, formerly of Izar, and I lead the future masters of the universe.

McCoy: How can we be powerful enough to wipe out a planet and still be so helpless?

Garth of Izar: You and Mr. Spock are to be my guests.
Kirk: Where is Mr. Spock?
Garth of Izar: Right here. Marta!
Marta: Why can't I blow off Just one of his ears ?
Garth of Izar: Stop that, Marta. Mr. Spock will think we're lacking in hospitality.

Garth of Izar: I may have you beaten to death.
Marta: No, you won't, because I am the most beautiful woman on this planet.
Garth of Izar: You're the only woman on this planet, you stupid cow.
Marta: Well, I'm the most beautiful woman in this galaxy!
Garth of Izar: You're repulsive!
Marta: I'm beautiful! And I'm intelligent too. I write poetry, and I paint marvelous pictures. And I am a wonderful dancer.
Garth of Izar: Lies! All lies! You are the greatest liar I have ever met! Let me hear one poem you've written.
Marta: If you like. "Shall I compare thee to a summer's day? Thou art more lovely and more temperate. Rough winds do shake the darling buds of May, and summer's lease hath all too soon..."
Garth of Izar: You wrote that?
Marta: Yesterday, as a matter of fact.
Garth of Izar: It was written by an Earth man named Shakespeare a long time ago!
Marta: Which does not alter the fact that I wrote it again yesterday!

Garth of Izar: Marta, my dear, won't you dance for our guests? That was not a request. Marvellous, isn't she, Captain?
Kirk: Yes, uh... incredible.
Garth of Izar: What is your reaction, Mr. Spock?
Spock: I find it, mildly interesting and somewhat nostalgic, if I understand the use of that word. Nostalgic. Yes. It is somewhat reminiscent of the dances that Vulcan children do in nursery school. Of course, the children are not so well-coordinated.

Garth of Izar: She's yours if you wish, Captain.
Kirk: Oh, uh... thank you. That's, um... very magnanimous of you.
Garth of Izar: You'll find that I am magnanimous to my friends and merciless to my enemies. And I want both of you to be my friends.
Spock: On what, precisely, is our friendship to be based?
Garth of Izar: Well, upon the firmest of foundations, Mr. Spock--enlightened self-interest. You, Captain, are second only to me as the finest military commander in the galaxy.
Kirk: That's very flattering. I am primarily an explorer now, Captain Garth.
Garth of Izar: And so have I been. I have charted more new worlds than any man in history.
Spock: And tried to destroy Antos IV. Why?
Garth of Izar: Well, I could say because they were actively hostile to the Federation.
Kirk: Yes, you could say, but that would be untrue.
Garth of Izar: Agreed.

Garth of Izar: I am master of the universe, and I must claim my domain.
Kirk: I agree there was a time when war was necessary, and you were our greatest warrior. I studied your victory at Axanar when I was a cadet. in fact, it's still required reading.
Garth of Izar: As well it should be.
Kirk: Very well. But my first visit to Axanar was as a new-fledged cadet on a peace mission.
Garth of Izar: Peace mission! Politicians and weaklings!
Kirk: They were humanitarians and statesmen, and they had a dream--a dream that became a reality and spread throughout the stars, a dream that made Mr. Spock and me brothers.
Garth of Izar: Mr. Spock, do you consider Captain Kirk and yourself brothers?
Spock: Captain Kirk speaks somewhat figuratively and with undue emotion. However, what he says is logical and I do, in fact, agree with it.

Garth of Izar: We, gentlemen, are that elite, and we must take what is rightfully ours from the decadent weaklings that now hold it.
Spock: Captain Garth...
Garth of Izar: Lord Garth!
Spock: As you wish.

Garth of Izar: By the way, I assume you play chess.
Kirk: Occasionally.
Garth of Izar: So do l. How would you respond to Queen to Queen's Level Three?
Kirk: You're aware that there are an infinite number of countermoves.
Garth of Izar: I'm interested in only one.
Kirk: I can't for the life of me imagine which one.
Garth of Izar: "For the life of me" is a phrase well chosen. It could literally come to that.
Kirk: Dead I am of no use to you.
Garth of Izar: But I can make you long for death, beg for death.
Marta: "In the midnight of November, when the dead man's fare is nigh, and the danger in the valley, and the anger in the sky." I wrote that this morning. Do you like it ?
Kirk: Yes, I think it's very good.

Marta: He's my lover and I have to kill him.
Spock: She seems to have worked out an infallible method for assuring permanent male fidelity. Interesting.

Kirk: Captain Garth...
Garth of Izar: Lord Garth!
Kirk: No, sir. Captain Garth, star ship fleet captain. That's an honorable title.
Garth of Izar: And I was the greatest of them all, wasn't I?
Kirk: Yes, you were.
Garth of Izar: Yes.
Kirk: But you're a sick man now, sir.
Garth of Izar: I have never been more healthy.
Kirk: No. No, think. Think back to what you were before the accident that sent you to Antos IV. Try.
Garth of Izar: I can't remember. It's almost as if I had died and was reborn. No, I... I can remember.
Kirk: You were the finest student at the academy, the finest star ship captain. You were the prototype, the model for the rest of us.
Garth of Izar: Yes, I do remember that. It was a great responsibility, but one I was proud to bear.
Kirk: And you bore it well. And the disease that changed you, it's not your fault. And the terrible things you did since then, not truly responsible.
Garth of Izar: I don't want to hear any more. You're weak, - and trying to drain my strength.
Kirk: No, I'm not. I want you to find what you once had,
to go back to the greatness that you've lost, Captain Garth.
Garth of Izar: I am Lord Garth! Master of the universe!

Garth of Izar: On your knees before me! All the others before me have failed. Alexander, Caesar, Napoleon, Hitler, Lee Kuan, Krotus! All of them are dust! But I will triumph! I will make the ultimate conquest !

Kirk: Garth, you have only a handful of men.
Garth of Izar: You do refuse to enter into the spirit of the thing, don't you, Captain? Perhaps you'd like a larger role in the ceremony. You could serve as human sacrifice.
Kirk: No, I wouldn't enjoy that at all.

Garth of Izar: Well, since there is no one mighty enough to perform this ceremony, we'll perform it ourselves.

Kirk: Mr. Spock, um, letting yourself be hit on the head, and I presume you let yourself be hit on the head, is not exactly a method King Solomon would have approved.

For the first and only time in the original series, Spock renders two people unconscious at the same time.

Kirk (or Garth as Kirk) mentions using the Cochran Deceleration to defeat the Romulan vessel near Tau Ceti. Presumably this is a reference to "Balance of Terror," as it is the only episode where the Enterprise defeated a Romulan vessel. However, Tau Ceti is never mentioned in that episode.

Garth mentions the dictator Lee Kuan, who was previously referenced by Spock in the second season episode "Patterns of Force."

What Changed in the Remastered Version
General improvements cited on the main series page. The planet Elba II gets the expected orbital upgrade and the poisonous nature of the atmosphere is much clearer. New footage is used of the Enterprise trying to cut through the force field: originally reused footage from "Who Mourns for Adonais?" was used.