Tintin is a comic book series created by the Belgian artist Hergé (Georges Remi. Take the initials, reverse them, and pronounce it in French). Since so much has already been written about it here, I'll content myself to writing about some topics that (I think) are interesting:
• In Tintin et les Picaros, Hergé gets Dupont and Dupond mixed up! See the scene where they are about to be shot. You can recognize them by their slightly different mustaches.
• Hergé played a cruel joke on us in Tintin et l'Alph-Art. He goes and dies just as Tintin is about to be made into a statue by having cement poured over him. (This book is out of print, luckily a friend had a copy)
• Where is Tintin from? We are told many times that he lives on Rue du Labrador, but what city and country? Look in Tintin au Tibet and you'll find in Chang's letter (if you can read Chinese) that the letter is from Hong Kong, to Ding Ding (which is pronounced more like Tintin than it looks) and is addressed to Bruxelles, Belge.
• A bit unrelated, but in Asterix chez les Belges we have Dupont and Dupond appear dressed as Gauls saying "Jules César est arrivé en Belgique", "Je dirai même plus: Cules Jésar est arrivé en Gelbique" (Julis Cæsar has arrived in Belgium, to be precise: Culius Jæsar has arrived in Gelbium) An observant reader will notice that when they speak, they have the same sort of speech bubbles Hergé used and they have the same lettering as was used in the Tintin books. (The speech bubbles in Asterix are oval, whereas in Tintin, they're rectangular, with curved edges)
• Tintin au Congo was re-published in colour in all languages except English. It was also edited (some unlikely scenes, like planting explosives in a rhinoceros, were taken out). It wasn't made into an English colour version because of its "racist overtones".
• Tintin au pays des Soviets is the only book where Tintin writes to his editor, though he consistently gives his profession as Reporter.
All quotes and names are from the Version Français in most cases; English translations would be welcome.