- "Something terrible is about to happen. I don't know what, but it's extremely important that you get out of this city a soon as you can! Save yourself. Remember, I love you."
- ―Kirby O'Neil[src]
Kirby O'Neil is the father of April O'Neil.
Kirby sent Pigeon Pete to deliver a message to April warning her to get out of the city. Instead, April and the Turtles got Pete to take them to where the Kraang were holding Kirby in order to rescue him. Kirby recognised the Turtles and told them what little he knew about the Kraang and their mutagen. The rescue mission was interrupted when Donatello discovered the Kraang had set a time bomb to disperse mutagen over the city. The Turtles freed Kirby from his cell, but the Kraang soon cornered them. Kirby took one of the Kraangs' guns and attacked the droids, telling the Turtles to save April and the city. He covered their escape, and was last seen being disarmed and re-captured by the Kraang.
- 101. Rise of the Turtles, Part 1 (as Kirby)
- 102. Rise of the Turtles, Part 2 (as Kirby)
- 109. The Gauntlet (as Kirby)
- 124. Operation: Break Out (as Kirby)
- 125. Showdown, Part 1 (as Kirby)
- 126. Showdown, Part 2 (as Kirby)
- 201. The Mutation Situation (as Kirby, and Kirby-Bat, no lines)
- 204. Mutagen Man Unleashed (as Kirby, photo)
- 211. Metalhead Rewired (as Kirby-Bat, no lines)
- 216. The Lonely Mutation of Baxter Stockman (as Kirby-Bat, no lines, and Kirby)
- 225. The Invasion, Part 1
- 226. The Invasion, Part 2 (as Kirby, and Kraangatized form, no lines)
- 309. Return to New York (as Kraangatized form, no lines)
- 313. Battle for New York, Part 2 (as Kraangatized form, no lines, and Kirby)
- 314. Casey vs. the Underworld (as Kirby, no lines)
- 318. The Deadly Venom (as Kirby)
- 325. Annihilation: Earth!, Part 1 (as Kirby, no lines)
- 426. Owari (as Kirby, no lines)
Total appearances: 18.