|“||You can take it from me. The truth? It's overrated.||„|
|~ Marty Wolf|
He first appeared when Jason Shepherd (a pathological liar and the main protagonist of the film) demands a ride to his school so that he can turn in his writing assignment to pass English class. During the ride, when Jason confesses that he is a liar, Wolf admits that he too is a compulsive liar, but a more professional one. After stopping at Jason's school, Jason heads off, not knowing that he accidentally dropped his report on the limo. Upon seeing it, Wolf initially attempts to give it back, but upon seeing how very good after reading it, he decides to keep it. This puts Jason in trouble with his parents and his teacher, forcing him to fail English class and undergo summer school to repeat the entire English class, as his parents refuse to believe that he had ever written his report and Wolf stealing his paper.
Later on, Jason and his best friend Kaylee found out that Wolf has plagiarized Jason's paper and is now planning it to turn it into a film after seeing a movie trailer of it. Outraged by this, Jason decides to confront Wolf, so he arranges himself and Kaylee to fly to Los Angeles, where Wolf is preparing for production for his movie in his studio. After having Kaylee to trick Wolf's secretary Astrid Barker into letting Jason into Wolf's office, Jason tries to convince Wolf to return the stolen paper to him and call Jason's parents and confess to them that he stole it. However, rather than doing so, Marty instead purposefully burns the paper with one of his cigars and his alcohol (much to Jason's shock) and orders Jason and Kaylee to be kicked out from the office.
Angered by this turn of events, Jason and Kaylee plan to inconvenience Wolf until he agrees to fess up, and a limo driver named Frank Jackson helps them out, stating that he was once a struggling rising star until Wolf demoted him to being a driver. They do so by committing several pranks such as dying his skin blue and his hair orange, sticking his phone earpiece with instant krazy glue, tricking him into going into a kid's birthday party, modifying his car's controls. Because of these, Marty start to lose support from his boss Marc Duncan (the president of the studios), who threatens to pull the production of Big Fat Liar if anything goes wrong. Jason then offers a deal to Wolf: he'll help him out if he gives the call to Jason's parents and confess to them about the report theft. After Wolf makes an astounding speech that inspires Duncan to green-lit the movie production, rather than calling Jason's parents, Wolf instead betrays Jason again by calling in security, who orders Jason and Kaylee to be sent home in disgrace.
Upset by this turn of events, Jason is about to accept defeat and is forced to call his parents to tell them the truth, but suddenly, Wolf's assistant Monty Kirkham arrives, having grown tired of her boss' abusive behavior and is offering to help him and Kaylee out. After arranging a meeting of several employees who were treated badly by Wolf, Jason and the others concoct one final plan to expose Wolf of his true colors.
The next day, as Wolf heads to the studio to being his shooting of the movie, his employees enact several mishaps to delay his arrival. As soon as Wolf finally arrives to the studio, he spots Jason, who has stolen his stuffed monkey Mr. Funnybones. After a chase across the studio, Marty finally recovers his toy monkey and taunts Jason for trying to make him confess about his theft, blurting out that he deliberately stole Jason's story and believing that no one has heard it. However, Marty is shocked to realize that several of his employees have recorded his confession with cameras from multiple angles, exposing him of his true colors to everyone in the studio (including Jason's arriving parents, who were brought over to the studio by Frank). Disgusted by Marty's actions for all the trouble of stealing the idea of his movie from a 14-year-old boy, Duncan fires Marty by telling him that this is the end of the line for him. Jason thanks Marty for teaching him the value of telling the truth before leaving with his parents, who finally believed their son.
Despite Wolf being fired, the production of Big Fat Liar continues on forward (even Frank becomes the starring actor of the new movie after being rehired by Duncan), proving to be an instant hit in the theaters. Jason is credited for writing the original story as Jason's parents are proud of him while Wolf is stripped of his career after Marty Wolf Pictures is shut down for good and now takes on a new job as a birthday clown. After being paid to attend a birthday party for a boy named Darren, Wolf is shocked to realize that Darren is the son of the Masher, a wrestler whose car he wrecked and insulted earlier. The Masher orders Darren to show his move called the Nutcracker, and Darren charges at Wolf by striking him in the groin, much to his dismay.
Marty Wolf is very arrogant, deceitful, and abusive in nature. He likes to lie a lot, believing that it can benefit him the most. He doesn't usually care for his employees; at one time, he demoralizes one of his elderly employees from going to his granddaughter's birthday party. In fact, the closest thing to something Wolf genuinely cares about is (bizarrely) his stuffed chimp Mr. Funnybones. These traits are what led to his downfall in the end when he is exposed for stealing Jason's paper to make his movie.
- The blue dye was actually blue tattoo ink that was sprayed in several layers on his body occasionally throughout the day to keep it topped up. According to actor Paul Giamatti, it was fairly easy to apply, but was a bit more difficult to get off, particularly his feet, for some reason. They stayed blue for several months.