The following is a gallery of Aaron Alexovich's concept art.
A Zoo Search Party Member from the unfinished episode, "Roboparents Gine Wild".
Coach Walrus from "Vindicated!".
A Tow Truck driver named "Kenny" from "Dibship Rising".
Frankenchokey from "Gaz, Taster of Pork".
A random Teacher from "Vindicated!".
Tavisha Wolfgarth-Simons from "Mortos Der Soulstealer".
A man in a Squirrel costume from "Mysterious Mysteries".
A Skool Guard from "Voting Of The Doomed".
A Science Team Guy from "Gaz, Taster of Pork".
A Group of Scientists from "Gaz, Taster of Pork".
A Rescue Trooper from "The Girl Who Cried Gnome".
Maurice The Puppy Man from "Mortos Der Soulstealer".
A Producer of Mysterious Mysteries (who turns out to be a small woman in a large body) from "Mysterious Mysteries".
The Skool Principle from "Voting of the Doomed".
Concept Art of President Man.
Poonchy's Mom from the unfinished episode, "Invader Poonchy".
Zim and GIR's clown disguises from the unfinished episode, "Nubs Of Doom".
A Security Guard from the unfinished episode, "Nubs of Doom".
A random girl from "Dib's Wonderful Life of Doom".
The General from the unfinished episode, "Invader Poonchy".
A Football Coach and Player from the unfinished episode, "Simon Says Doom".
Mr. Dwicky from "Vindicated".
X-Rays of the Kids from "Dark Harvest".
Willy from "Voting Of The Doomed".
Woozly from the unfinished episode, "Return of Keef".
A weird clown from "The Girl Who Cried Gnome".
A Cheese Log Vendor from the unfinished episode, "Nubs Of Doom".
A Bus Driver named "Busman" from "Dibship Rising".
Concept Art of Bloaty the Pizza Hog.
An alien-attired actor from "The Frycook That Came From All That Space".
Cyborg Zombie Soldiers from "Zim Eats Waffles".
Mr. Sludgey from "The Most Horrible X-Mas Ever".
Future Membrane from "Dib's Wonderful Life of Doom".
Dibship from "Dibship Rising".
Dinky from the unfinished episode, "Roboparents Gone Wild".
A Zootch Alien from "Hobo 13".
A Nub Bubbins Alien from "Hobo 13".
An implied Alien couple from "The Frycook That Came From All That Space".
A group of Alien species from "The Frycook That Came From All That Space".
A strange-looking Alien from "The Frycook That Came From All That Space".
Random Alien species from "The Frycook That Came From All That Space".
A group of random species from "The Frycook That Came From All That Space".
Another group of random species from "The Frycook That Came From All That Space".
A group of Irken Elites from "Tak: The Hideous New Girl".
Giganto-Baby from "Plague Of Babies".
Tallest Puppets from "Tak: The Hideous New Girl".
A variety of Halloweenies from "Halloween Spectacular of Spooky Doom".
Line-Art of Zim bursting out of the Nightmare World from Dib's head from "Halloween Spectacular Of Spooky Doom".
Zim's Horrible Human Disguise from "The Girl Who Cried Gnome".
An obese GIR from "Halloween Spectacular Of Spooky Doom".
A variety of Zim's disguises.
A variety of Dib concept art.
A variety of Gaz concept art.
Cthulu in its First Stage from the unfinished episode, "The Trial".
A young Zim from the unfinished episode, "The Trial".
Young Tallest Red or Purple from the unfinished episode, "The Trial".
Various alien monsters with Zim on top of them from the unfinished episode, "The Trial"
Horrible Cartoon Kid from the unfinished episode, "The Trial".
A Vortian Guardsman from the unfinished episode, "The Trial".
Zim and Lard Narr among other scientists from the unfinished episode, "The Trial".
Zim in his Elite uniform from the unfinished episode, "The Trial"
Red or Purple in their Elite uniform from the unfinished episode, "The Trial".
Zim blindfolded from the unfinished episode, "The Trial".
A different Irken Control Brain design from the unfinished episode, "The Trial".
Tallest Miyuki from the unfinished episode, "The Trial".
Tallest Spork from the unfinished episode, "The Trial".
Concept Art of Rikki Simons.
A Deteriorating Zim from the unfinished episode, "Ten Minutes to Doom"
First Page of Gaz's Robot Toys from the episode, "Gaz, Taster of Pork".
Second Page of Gaz's Robot Toys from the episode, "Gaz, Taster of Pork".
Third Page of Gaz's Robot Toys from the episode, "Gaz, Taster of Pork".
Easter Platypus Concept Art from the episode, "The Most Horrible X-Mas Ever".
A female Irken Elite from "Tak: The Hideous New Girl".
Another Irken Elite from "Tak: The Hideous New Girl".
A male Irken Elite from "Tak: The Hideous New Girl".
Older Gaz from "Dib's Wonderful Life of Doom".
Mortos from "Mortos Der Soulstealer".
The Girly Rangers from "The Girl Who Cried Gnome".
A 4-year old girl from the unfinished episode, "Simon Says Doom".
A 4-year old boy from the unfinished episode, "Simon Says Doom".
Another 4-year old girl from the unfinished episode, "Simon Says Doom".
Another 4-year old boy from the unfinished episode, "Simon Says Doom".
An obese kid or baby from the unfinished episode, "Simon Says Doom".