Zak is best known in Flanders as the house cartoonist of the left-wing, progressive newspaper De Morgen. With his simple line drawings he offers an ironic look at current events. Originally he attacked specific celebrities which he caricatured in cartoons as well as more comic strip-based stories. Later he favored one-panel gag cartoons more and became less direct in his targets. Most of his cartoons poke more fun at topical situations rather than name names. It gives his work a more timeless approach, which explains why he is able to bring out annual pocket agenda's ('De Zakagenda') compiling his older work.
He was born in 1948 in Gent as Jacques Moeraert. His pseudonym "Zak" has a double meaning in Dutch: it's both the word for "sack", as well as a vulgar insult to somebody. Zak was initially a bookkeeper, but switched to cartooning at the age of 25. Together with his friend Quirit, he published his first cartoons in Johan Anthierens' satirical magazine De Zwijger. He published the comic book 'Hoe kwamen onze jongens ertoe met de Romeinen te collaboreren?' (1983) and together with columnist Bert Verhoye, he drew 'De Vliegende Paap' (1985), a satirical comic book about pope John Paul II, published in the same year His Holiness visited Belgium. Along with Gal, Quirit, Peter De Roy, Jan Bosschaert, Erik Meynen, Benoît and Jan De Maesschalk he was one of many cartoonists who made a graphic contribution to Johan Anthierens' anti-royal book 'Brief aan een postzegel' in 1990.
When De Zwijger was disestablished in 1984, Johan Anthierens' brother Karel guided Zak to the left-wing newspaper De Morgen. In those early days De Morgen was often understaffed. In case an issue lacked enough photographs, Zak was called in to make some extra cartoons. Some editions had up to five or more drawings by Zak instead of the usual one or two. When the newspaper was on the brink of bankruptcy, he designed posters for benefit performances to help it out its financial troubles. Eventually it did establish itself on the Belgian newspaper market, with Zak as its house cartoonist.
His work also appears in De Tijd and the Dutch newspapers De Volkskrant, De Limburger and De Groene Amsterdammer. He also draws for the Dutch Ministry of Defense and the monthly magazine of the Dutch Railways. In France readers can enjoy him in Le Point.
Zak is best known for his ironic, tongue-in-cheek style. He always finds a way to joke about current topics, no matter how depressing they may be, and thereby reduces them to their right perspective. Earlier in his career, Zak often made jokes about specific politicians, like Prime Minister Wilfried Martens, Pope John Paul II, Belgian king Baudouin and Zaïrese dictator Seko Seko Mobutu. His cartoons irritated Belgian politician and former Prime Minister Paul Vanden Boeynants so much that he frequently wrote angry letters to De Morgen. Later Zak's cartoons evolved to more timeless and less specific jokes about regular people. Since 1993 he prefers the one-panel gag cartoon format over making actual comics too. Zak explained in a 1996 interview with De Groene Amsterdammer that, as he grew older, he just got over his idealism. He felt he was arrogant to think he had "anything interesting to say" and therefore refused to caricature specific politicians anymore. Rather than spend attention to hypocrites who just want to get votes he focuses on average people, whom he deems far more interesting. In the same way Zak quit drawing comics too, because he didn't fancy himself a great narrator. However: he still gets his inspiration from daily events. He just sits back and witnesses every media story with a certain distance, necessary to remind people to not take everything so seriously. And if he has to reference a certain celebrity in function of a joke he tries to do so by having regular people discuss the matter.
Since 1997 Zak publishes an annual pocket agenda, nicknamed 'Zakagenda', which compiles several of his best cartoons. In the early 1990s he also made a series of animated shorts for the production company ID-tv, which starred an unlucky character named Knito.
Zak has won the Royale Belge Prize for Best Press Cartoon (nowadays the Press Cartoon Belgium Prize) up to three times: in 1999, 2003 and 2015. His 2003 winning entry showed nuclear weapon inspectors in Iraq being saluted by soldiers who carry invisible weapons. This was a nod to the later proven fact that Iraqi dictator Saddam Hussein didn't have any weapons of mass destruction. In 2015 he won with a cartoon about the Syrian refugee crisis. The drawing showed a beach full of boat refugees, while a mother disappoints her child by saying: "We already went to see the boats come in, yesterday." Zak also received the Ark Prize for Free Speech (2000), the Inkspotprijs (2001), the BeNe Prize for Best Cartoon in the Dutch-language press (2003) and an honorary doctorate from the Brussels University in 2009.
On 2 September 2008, one of Zak's cartoons caused controversy in France. The drawing depicted coffins of dead soldiers with medals stuck to them. Two characters walk by and comment: "Even from Afghanistan the French come back home with medals", referring to both the death of 10 French soldiers during the Afghan War, as well as the Olympic Games. French senator Simon Loueckhote, who is related to one of the victims, asked President Sarkozy to register a complaint against De Morgen for publishing this cartoon.