Mark is an alien Prince from the planet Yugopotamia, a place where everyone behaves and likes things opposite of humans: For instance, they find garbage and manure to be delicious, and are terrified of cute things such as Poof or The Gigglepies. Mark's parents, King Gripullon and Queen Jipjorrulac, love their son very much, although they still arranged a marriage to the terrifying and beautiful (ugly to Mark) Princess Mandie. Eventually Mark fled to Earth where he uses his Fake-i-fier to remain disguised as a Human boy. Mark is greatly in love with Vicky. He likes earth a lot and is disguised as a teenage boy.
His species is generally warlike and loves painful or disgusting things, which explains why Mark fell in love with Vicky the instant he saw her; many of his appearances involve his attempts to woo her. Because Timmy has proven invulnerable to most of the things that harm Yugopotamians---such as chocolate, flowers and teddy bears---they erroneously believe him to be a great warrior. He has a fiancé named Mandie (second syllable pronounced like die) whom he fled to Earth to avoid marrying; he currently lives in the Dimmsdale dump, disguised as a human. He is one of the few people allowed to know about Timmy's fairy godparents since he's not human, therefore outside of Da Rules.
In his human form, Mark appears as a boy around Timmy's age with red eyes, curly black hair, and a green hat and pink shirt with the same symbol alien-Mark has on his chest. If something nice happens to Mark, for instance getting kissed by a girl, his fake-i-fier will malfunction and he will lose the ability to remain in human form.
In the episode "King Chang", Mark changed his human disguise form to that of a hunky young teenager named Justin Jake Ashton, he does so that way he can actually date Vicky on earth, who he is in love with. Unfortunately for him, his fake-i-fier malfunctioned just before the date, and Vicky dumped him.
Mark first met Timmy when he wished for an alien monster for him and his friends, Chester McBadbat and A.J., to play with. Wanda Fairywinkle-Cosma and Cosmo Cosma, not being very good at making up monsters, "borrowed" one from Yugopotamia, which happened to be Mark. Upon arriving, he threatened to suck out the trio's brains with bendy straws, but believing him to be an advanced toy, the threat wasn't taken seriously, much to his confusion. Soon afterward Vicky burst in, frightening the kids. Seeing she had so easily instilled fear into the three that he failed to even faze, he immediately fell in love with her.
Thinking he was a kid in a costume, Vicky dragged Mark downstairs, where she ordered him to make her a chocolate shake. This caused him to fall for her more, since chocolate is the deadliest substance to Yugopotamians. While fixing his crush her meal he was attacked by Chester and A.J., still thinking he was a toy. He captured them easily and was about to suck their brains out when Timmy came in, armed and ready to fight. Timmy lost as well, but before Mark could do anything King Gripullon and Queen Jipjorrulac came to the front door, disguised as humans, and forced their son back home.
After returning home Mark became depressed without Vicky. On his birthday he began grieving when Cosmo showed up, fulfilling Timmy's desire to get Vicky "a million million" miles from him. The green haired fairy showed Mark a fake message from Vicky, begging him to come take her away. All to eager to comply, Mark left with Jeff and Eric to retrieve her.
Landing on Earth, they quickly tracked Vicky and sprayed her with sleeping gas, then convinced Mr. Turner that she was leaving for Europe. They then returned to their home planet, only to find Timmy waiting, demanding her back. Unwilling to relinquish his love, he challenged Timmy to "ditch eh fat", which Timmy immediately accepted, thinking it was some flower skipping horror. It was actually Death Combat, which Mark chose to have in the Yugopotamian War Arena. Despite struggling against Cosmo and Wanda's magic, Mark eventually got the upper-hand and fired a large gun...and missed.
Timmy then got to choose the arena, to which he picked Flappy Bob's Happy Camp Learn-a-Torium. Overwhelmed by the sweetness and bright colors, he surrendered. Feeling sorry for him, Timmy spared his life, promised to give him Vicky when he turned sixteen, and gave him a Smack-a-Mole machine as a birthday gift. Mark vowed to return once he had mastered the machine.
Mark was briefly brought to Earth by Timmy and Vicky's reset watches, but this event was quickly wiped out of the timeline.
The following Halloween, when the royal ship was near Earth, Mark noticed the planet was going to explode, and went down with Jeff and Eric in Candy Protection Suits. While they quickly found Vicky, Cosmo prevented him from leaving on Timmy's orders. When the then in place wish was reversed, Mark recognized Timmy and accused him of preparing for war (since so many Earthlings were gathering candy). Timmy went along with this, threatening Yugopotamia. Panicing, Mark and his friends beamed back up and launched the P-Bomb at Earth. This was exactly what Timmy wanted, as it was really a piñata full of candy. Mark was temporarly saddened by Vicky's supposed death...until it was revealed that they had her cloned.
Soon afterward, The Gigglepies invaded Yugopotamia, capturing and enslaving most of its inhabitants. Mark escaped, and traveled to Earth to recruit Timmy to battle them. He planned to fight alongside him, but was sidetracked by Vicky. While Timmy was freeing Yugopotamia, Vicky was forcing Mark to do backbreaking labor, which was the highest expression of love on his planet. Vicky took advantage of this by using him to make money. By the time Timmy returned, Vicky was rich, and Mark planned to stay, until Vicky hugged him. Horrified by this action, he quicky returned home.
Mark eventually returned to Earth and offered to skate with Trixie Tang after Timmy wished there were no more boys on Earth. He was soon wished out of existence by the following wish. When it was unwished, he reappeared in front of the White House, where he loudly declared himself "a hostile alien bent on world domination", which promptly got him arrested. He somehow escaped custody.
Shortly afterwards, Mark was forced into a marriage with Princess Mandie so the Yugopotamians and the Bodacians could forge a military alliance. Mark, however, was repulsed by Mandie's appearance, and fled to Earth, where he begged Timmy to let him hide there. Timmy agreed, and he began attending school disguised as a human student, while parking his ship in the Dimmsdale Dump. Eventually, however, Mandie found him and froze Cosmo and Wanda in carbonite to prevent their interference. After a long chase, Timmy and Mark tricked her into taking a transformed Denzel Crocker instead.
Mark had Timmy over for dinner soon afterward, where he served him healthy food for dessert, to Timmy's horror. When Timmy wished for just dessert, Mark remained the only one thin due to his healthy choices. When the Earth began drifting toward the sun, he planned to flee, but the now bloated Timmy stopped him. He then sat on him until he gave up the last of his healthy food.
When F.L.A.R.G. started, Mark fell into a depression at being unable to attend. Timmy decided to give him everything he needed to celebrate the holiday. Mark spent the next five days putting Timmmy through a painful holiweek, accumulating in Goodbye...where he planned to blow up the Earth. Timmy convinced him he couldn't blow up the Earth since it was now his home. Mark agreed, and redirected the missile(with some more convincement from Timmy so his appendix would not destroy the Earth) to somewhere else, but we then find it hit Fairy World.
Shortly after his Fakeifier short circuited, allowing Mandie to find him. In a panic, Timmy wished everything was like a child's puzzle book he was reading. As a result, Mark spent a while disguised as a trophy until Mandie threatened to blow up Dimmsdale Elementary School unless Mark surrendered. Mark complied, but she refused to spare the school. Fortunately, by that time Cosmo and Wanda recovered their wands and wished Mandie away.
When Timmy wished the world into a futuristic society, Mark was able to walk freely. He joined Timmy in defeating the Big Brain.
Mark eventually celebrated his one year anniversary on Earth with Cosmo, Wanda, Poof, and Timmy, where he revealed he was dating Vicky. However, the group was abducted by Grippulon, who explained he was targeted by an unknown assassin. Mark agreed to temporarly take the throne, sending his father to Earth disguised as Timmy while his mother but, being preoccupied trying to get Poof back from Mr. Turner and Mrs. Turner, he did nothing, allowing Mark left for a spa date. Immediately after taking the throne Mandie revealed herself as the assassin and forced Mark to marry her, shrinking the fairies so they couldn't interfere. She then promptly tossed her husband and Timmy into jail. The pair escaped and fled to Earth, with Mandie in pursuit. Disguising himself as Justin Jake Ashton, Vicky's boyfriend, he got Vicky and Mandie to fight, which Vicky won. Mark hugged his girlfriend, causing his true form to be revealed, which led to Vicky dumping him. Mandie was arrested and sent to jail, and Mark chose to stay on Earth until it was time for him to truly take the throne.
Shortly after Mandie was arrested, Mark's Fakeifier began to malfunction once more. He ran to Timmy to get it fixed, to go through several ordeals. Finally, Timmy had Mark pose as Poof's alien mom, allowing them to get him back. They then fixed the Fakeifier.
Not long after his Fakeifier began malfunctioning again. Rather than go to Cosmo and Wanda, he opted to travel back to Yugopotamia to retrive one from his parents. Unfortunately, he arrived just as The Darkness was invading Yugopotamia. With only one royal escape pod left, King Gripullon and Queen Jipjorrulac sent their son back to Earth. He landed right on top of an Eliminator impersonating him. After taking the destroyed robot's Fakeifier as his own, he explained the situation to Timmy and his fairies. The group traveled to Fairy World to tell Turbo Thunder, who they believed to be the true chosen one, but arrived just after Jorgen Von Strangle had banned him from the realm. Jorgen took them to the Cave Of Destiny, where they discovered a second part of the prophecy, written in Yugopotamian. This one called for Timmy to find the Wind Wand on the dark side of the blue moon to vanquish The Darkness once more. Shortly afterwards the Eliminators invaded Fairy World, capturing the world's fairies. Timmy and Mark barely escaped through a portal in the cave's wall.
Timmy decided to find the wand, asking Mark to come with him. The Yugopotamian prince refused, however, preferring to stay at home and eat. However, when Timmy got attacked by Eliminators disguised as his parents, he had a change of heart and decided to help him. After being attacked by Eliminators impersonating Chester, A.J., and Trixie, and realizing they had no ship since Mark's was on Yugopotamia, they decided to seek help from more unusual sorce. Going into the Crocker Cave, they asked Timmy's teacher for help. Crocker agreed after Timmy anticlimatically admitted he had fairies and let them use his telescope. There, they saw The Blue Moon of the Vegan System, where the Wind Wand rested. Crocker also provided a rocket for transportation, but launched it before anyone was on it. Unfazed, Timmy asked for a laptop, an internet connection, and a whoopie cousin, which Mark readily provided. The resulting TooYube video had the desired effect: getting Dark Laser to come to Earth in a fit of rage. Timmy merely pushed him back on his ship and summoned Vicky just before taking off. After a quick explanation, and a few promises, the group began heading toward the Blue Moon.
The group decided to stop at a canteen at the neighboring planet Frigidarium. It turned out to be a trap by the Eliminators. The resulting fight was undeniably one sided, with Crocker, Vicky, and Dark Laser getting captured. Mark and Timmy ran out, only to run into Turbo Thunder, demanding to know where the Wind Wand was. Timmy agreed on the condition that he would take him and Mark with him. Thunder promised, but after Timmy told him the location he abandoned them to the Eliminators. Mark saved their lives by swallowing Timmy and stowing away on the bottom of Thunder's ship. When the reached the Blue Moon he coughed his friend up.
After Timmy earned the Wind Wand and proved himself the true Chosen One, the Darkness appeared. Fortunately, at that point so did all to Timmy's now freed friends. The Darkness responded by attempting to swallow them all. Timmy, realizing what he had to do, sacrificed himself. After temporarily mourning his friend, Mark attempted to take advantage of the grieving Vicky, with predictably painful results.
After Timmy was rescued from The Darkness, Mark welcomed him back to Earth, interrupting an attempted kiss between him and Trixie. He then geared up to fight The Darkness, but was soon captured by invading Eliminators. After The Darkness became The Kindness, he was restored. He then attended a large party in celebration.
Like all Yugopotamians, he fears nice and cute things like flowers and chocolates. Also, kisses and hugs from girls make's his fake-i-fier malfunction. It was also revealed that he fears soy cubes which Gary and Betty offered him when they popped out of the smack a mole game which Timmy gave him as a present. This was revealed in the episode Totally Spaced Out.
When Mark first met Vicky he fell in love with her nasty attitude and unattractive appearance, as Yugopotamian's love opposites he actually found Vicky to be quite desirable. Vicky seems oblivious to his attraction at first, but later he uses it as a means to accomplish her work easier by using him as a loyal servant. Vicky also does not realize Mark is an alien, and thinks that he is a foreign exchange student from Europe who is wearing a costume all the time. Mark was going to go on a date with Vicky while using his fake-i-fier to change his appearance to that of a human teen, but his fake-i-fier malfunctioned and he returned to normal, causing Vicky to dump him. This romantic angle has not been touched upon since, and Mark is seen actively trying to pursue normal Earth girls in recent episodes.
Mark dislikes and fears Princess Mandie, and ended up leaving her on the altar after his parents tried to force him to marry her. Because of the nature of Yugopotamians, Princess Mandie's beauty is a bad thing. Eventually, Princess Mandie and Mark were married, but it turned out it was just a ruse to take over his planet. Mark Chang returned to Earth again and Mandie followed, but she was defeated by the one woman in the universe even nastier than she: Vicky.