The alien Kodos, who frequently appears in The Simpsons, is named after the character in this episode.

The band at Leighton's party plays the Star Trek theme.

Grace Lee Whitney makes her last appearance on the show, with no dialogue, as she walks by Lenore on the bridge.

Spock: How did you know this lady was coming on board?
Kirk: I'm the captain.

McCoy: When the man on top walks along his street, the chain of command is often a noose.
Spock: Spare me your philosophical metaphors, Doctor.

McCoy: This is the first time in a week I've had time for a drop. Would you care for a drink, Mr. Spock?
Spock: My father's race was spared the dubious benefits of alcohol.
McCoy: Oh. Now I know why they were conquered. What are you worried about? Jim generally knows what he's doing.
Spock: It was illogical for him to bring those players aboard.
McCoy: Illogical? Did you get a look at that Juliet? That's a pretty exciting creature. Of course your, uh, personal chemistry would prevent you from seeing that. Did it ever occur to you that he might like the girl?
Spock: It occurred. I dismissed it.
McCoy: You would.

Lenore: Star light, star bright. I wish I may, I wish I might. Do you remember that, Captain?
Kirk: It's very old.
Lenore: Almost as old as the stars themselves.

Lenore: (to Kirk) All this power, surging and throbbing, yet under control. Are you like that, Captain?

Kirk: Worlds may change, galaxies disintegrate, but a woman... always remains a woman.

Uhura: (singing) The skies are green and glowing
Where my heart is
Where my heart is
Where the scented lunar flower's growing
Somewhere beyond the stars
Beyond Antares
I'll be back, though it takes forever
Forever is just a day
Forever is just another journey
Tomorrow a stop along the way
And let the years go fading
Where my heart is
Where my heart is
Where my love eternal is
Waiting
Somewhere
Beyond the stars
Beyond Antares

Spock: Someone tried to kill him.
McCoy: Could have been an accident.
Spock: You should be told the difference between empiricism and stubbornness, Doctor.

Spock: Even in this corner of the galaxy, Captain, two plus two equals four. Almost certainly, an attempt will be made to kill you.

McCoy: What if you decide he is Kodos? What then? Do you play God, carry his head through the corridors in triumph? That won't bring back the dead, Jim.
Kirk: No. But they may rest easier.

Kirk: Are you sure you didn't act this role out in front of an audience whom you blasted out of existence without mercy?
Karidian: I find your use of the word mercy strangely inappropriate, Captain. Here you stand, the perfect symbol of our technical society--mechanized, electronicized... and not very human. You've done away with humanity, the striving of man to achieve greatness through his own resources. We've armed man with tools. Striving for greatness continues. But Kodos... Kodos, whoever he was...
Kirk: Or is.
Karidian: Or is. Kodos made a decision of life and death. Some had to die that others might live. You're a man of decision, Captain. You ought to understand that.

Karidian: Did you get everything you... wanted, Captain Kirk?
Kirk: If I had gotten... everything I wanted... you might not walk out of this room alive.

Lenore: There is no mercy in you.
Kirk: If he is Kodos, then I've shown him more mercy than he deserves. And if he isn't... then we'll let you off at Benecia, and no harm done.
Lenore: Captain Kirk. Who are you to say what harm was done?
Kirk: Who do I have to be?

McCoy: In the long history of medicine, no doctor has ever caught the first few minutes of a play.

Kirk: You'll never get off the ship.
Lenore: Then it will become a floating tomb, drifting through space with the soul of the great Karidian giving performances at every star he touches.

Spock checks the computer records and asks for any points of correlation between Karidian, Kirk, Riley, and Leighton. However, it would be impossible for Karidian to have any connection to the other three, because he didn't "exist" at the time of the Tarsus 4 massacre and any fake records he created wouldn't have connected him to the other three. Yet Spock connects him to the others anyway.

The Conscience of the King

The title of the episode comes from Shakespeare's Hamlet - the same play the Karidian Players perform for the crew of the Enterprise.

This is the first and last time that Kirk orders a "Double Red Alert."

What Changed in the Remastered Version
Along with the usual HD improvements, Planet Q gets a nice orbital upgrade and there are several different angles of the CGI Enterprise in flyby. Curiously, several shots are not upgraded, including the exterior matte scene shot through the Leightons' window (a reuse of the Mojave desert scene from "The Cage"/"The Menagerie") and the phaser shot that kills Karidian. The opening credits run with the original music, rather then the remastered version.