Officer X was an animal control officer who worked for the Metropolitan Sub Bureau of Animal Control and Pretzel Cart Regulation. The zeal with which he applies to his job can be considered obsessive, given how he tracks the penguins through the streets and sewers of New York with his van. He doesn't like penguins because he considers them to be "nature's rule breakers," because although they're technically birds, they swim instead of fly. He uses a cow prod, smoke bombs, a tag shooter, snares and various other booby traps to catch animals. His own mom never told him his real name because it was classified. He used to drive a red animal control van with lots of gadgets on it, but then he lost his job - and others since - thanks to his obsession with the Penguins.
Mr. X first appears trying to capture Max, a stray cat the penguins previously befriended. When they crossed paths, he soon proves a worthy opponent to the penguins, managing to beat their attempts to defeat him, with his abnormal skills and abilities. With their options running out, they hide Max by disguising him as a wild cat. Mr. X buys one minute, but then Max accidentally blows his disguise the next while gloating. Luckily for him, Alice stops Mr. X from catching him by putting him with a female Red Rhodesian Slasher. Not one to give up easily, he decides to sit and watch till Max tries to bail. However the penguins manage to outfox him by disguising Mort as a rabid chihuahua to lure away from the cage then switching Max with the real wild cat, who attacks X.
He next appears after the penguins are spotted, and animal control is called. He quickly traps them with his fish trap, only for them to escape by blasting a hole through the bottom. It is then revealed that his van has laser drilling abilities. After it lands, the penguins flee through a topside tunnel. However, it manages to follow them up a nearby staircase. After a brief struggle, they disable the van. But Mr. X is still on their trail. They almost lose him by diving back into the sewers. It turns out he is already in front of them, causing Skipper to shout "Sweet Dixy Dridles! How much are they paying this guy?" Quickly the penguins pull a last minute plan and cut the sewage pipes above Mr. X to knock him down. It fails, leading to Mr. X trapping them. But while he was gloating, a doll blasts out of the clogged pipe and into Mr. X's face, followed by sewer water. Their plan did work, and they escaped. Afterwards Mr. X went on a rampage of destruction round the city, and as such lost his job.
He next appeared after some of Rico's roach friends were being bothered by him. After hours of waiting, they found out it was him. He captured three of them, then revealed he still had some of his old gadgets because he knew they'd cross paths again. Mr. X was ready to enact his revenge, only for Private to cause the roaches to crawl into his suit causing him to run off. He also lost his mustache in this episode.
His next appearance was during a heat wave. The penguins got rid of Alice so they could go swim in the East River, only her replacement turned out to be Officer X (Now Zookeeper X). Remembering the penguins he went over to them, and told them that they should have finished him off the last time they clashed, as now Mr. X was the boss, and he was ready for revenge. The penguins tried to escape at night only for Mr. X to catch them. Next they tried to tunnel out, only for X to catch them again. Next they tried using a secret back up air vent that not even Alice knew about, only for X to catch them a third time. They ran one way only to bump into X, then the opposite way, only to run into X again. They jumped down and into the sewer only to meet X again. They jumped out and jumped out and over all wall, only to be caught by X again.
Getting desperate, they built a flying machine, and got away, it was all going well, till Private pointed out that it was possible that he had anticipated their plan, and had stowed away in the cart, just below them, and that it was odd that when they ran around the zoo collecting parts, that they didn't see him, panicking the penguins tried to open the cart but were to scared in case Mr. X was actually in there, and he was about to jump out and say on of his witty one liners.
Annoyed at their silliness, Private opened the cart to show Mr. X wasn't in there. Relieved, they relaxed only to find out that Mr. X was hiding in the umbrella. He took out his taser and then knocked them off the cart. Skipper caught Private while Kowalski and Rico fell back down into their habitat in the zoo. Private jumped back onto the cart, only to find Mr. X there. The crazed man thought he was finally going to get his revenge when Skipper interfered and caused the till of the cash register that they were using as a steering mechanism, to knock him off, he fell and landed on Alice's taxi and was last seen as it drove away.
He next made a cameo appearance in Rat Fink.
His next appearance was in A Kipper for Skipper when Kowalski, Rico and Private were arguing over the fish Mr. X captured the three of them. Luckily, they were able to defeat him by dropping a bowling ball on him.
He was briefly seen in Goodnight and Good Chuck, in which a video revealing all of the penguins' covert operations were broadcasted worldwide. Officer X watched the news segment in Times Square and triumphantly told anyone who would listen that "I told you!" and "I'm not crazy!" He then calls his mother and tells her to turn on the TV to prove his sanity. Unfortunately, everyone else who watches it believes it to be a news hoax due to the sheer impossibility of the scenario and the amusing antics of the penguins in the video, and Officer X drops to his knees and cries out in despair when still no one believes him.
He was then seen stacking shelves in Snowmageddon as Storekeeper X. When Skipper and Marlene went out for a snack run and the snowstorm hit, trapping them all in the store, it was a simple matter for X to capture Skipper, who he tied up with a licorice whip, put under a plastic crate, and sat on it while calling animal control. They didn't believe him, but he was prepared to bring Skipper back just the same even if it meant trudging through the snowstorm. Marlene helped break Skipper free, and one can only presume that after the damage done to the store that he was fired again.
He is the most skilled human the penguins have faced. He manages to track Max the cat to the zoo and through it by scent, lace the outer perimeter with booby traps, and he has also shown superhuman attributes on occasion able to crush a metal cage with one hand and take down Joey the Kangaroo with only 2 moves, something the penguins could never do. He was even able to survive a four-hundred-foot drop with no apparent harm. Mason also said that he is not human.
Officer X is also highly skilled with his gadgets, and has a great arsenal of weaponry at his disposal; his apparent favorite is his taser. He is also shown to be highly intelligent, capable of constantly out-thinking the penguins and anticipating their plans.
He also seems to make puns which the penguins and Marlene seem to think he could've dug a little deeper.