John Henry Irons was first seen in the episode "Prototype."

Natasha: You're gonna be home on time for dinner tonight?
John Irons: What are we having?
Natasha: Pork chops and bean curd in a cilantro sauce.
John Irons: Argh!
Natasha: (chuckles) Hey, you're the one who bought grandma a California cousin cookbook.
John Irons: Maybe I should be building myself a cast-iron stomach.

Robber: (to John Irons) Look! It's a dead Samaritan. Say "good night," chump!
Superman: Good night, chump!

Superman: Metallo!
Metallo: In the flesh!

Metallo: Remember how you left me, Superman? Buried in rock. I couldn't move! I couldn't see! I couldn't hear! But I could think! And all I thought about was how I was going to make you pay! Goodbye, hero.

Metallo: (to John Irons) You ought to be paying attention my friend! The tabloids will be all over you! You're about to become famous. The man who watched Superman die!

Metallo: Somebody speak up! Or I'll tear this neighborhood apart! Brick by brick.
Teen: We got nothing to say to you, Robo-butt.

Metallo: Now, where is Superman?!
Teen: Try the planet Krypton!

Metallo: Well, what have we here?
Steel: Call me Steel.
Metallo: Steel? Metallo. (bows) The meeting of the metals! Well then, Mr. Steel, may the best alloy win.

Natasha: Come on, Superman! This ain't no tanning salon!

Natasha: He's got Superman. He's gonna kill 'em!
Steel: Not on my watch he's not!

Superman: Well, Steel, you're gonna be getting this a lot, so you might as well hear it from me first.
Steel: What?
Superman: Thanks!

Metallo: Sorry, Steel. I've still got some business in the 'hood!

In "Action Figures," which featured Metallo's first reappearance before this one, he is completely stripped of his synthetic skin. When Metallo appears here, he has the ripped mask on his face again.

"Monkey Fun"

Bibbo: I remember one time we was fighting this big monkey.

Bibbo was referring to Titano.

"Action Figures"

Metallo: Remember how you left me, Superman? Buried in rock. I couldn't move! I couldn't see! I couldn't hear! But I could think! And all I thought about was how I was going to make you pay!

Metallo is referring to the time when Superman left him buried under solidified lava without his kryptonite battery.