Les aventures de Tintin - 1957 Le crabe aux pinces d'or 1-6 is rated/received certificates of:
Belgium:KT
Le crabe aux pinces d'or - 1947 is rated/received certificates of: Belgium:KT UK:U (video rating)
I am presuming you refer to Tintin, the picture book/cartoon strip series, as opposed to the recent Tintin movie which came out in 2011. I will attempt to answer this in order of appearance in the original series of books. Oftentimes, the importance of a character correlates with the order in which he (or she) appeared in the series. Tintin, of course, is the main character, the young reporter with motives and morals strongly ressembling "(boy) scout's honor". Tintin's ever-faithful dog, Snowy (known as Milou in French), appears virtually a few frames after Tintin in "Tintin in the Land of the Soviets" (the first ever Tintin strip). He is a terrier (some claim even more specifically that he is a wire fox terrier) who may occasionally let himself get into trouble, but more often than not follows a moralistic ideal similar to Tintin. He is often quick to help his master out of difficult situations, and is rarely far from Tintin's side. The first secondary "main" character to recurringly appear in the series is Captain Archibald Haddock (in French, the phonetically similar Capitaine Archibald Hadoque). We first see him as the drunken "captain" of the Karaboudjan in "The Crab with the Golden Claws" ("Le Crabe au pinces d'or", one of the books from which the recent Tintin movie adapted its storyline). Once he realizes his crew has mutinously taken over his ship, he quickly sobers up and fast becomes Tintin's most constant human ally. His alliance to Tintin is sustained for the remainder of the book series, a literal "friend for life". The next secondary "main" character would be the hard-of-hearing scientific inventor Professor Calculus, known in French as "Tryphon Tournesol", but whose name in English escapes me at this moment. He appears suddenly in "Red Rackham's Treasure" (or "Le Trésor de Rackham le rouge") amidst a bunch of people claiming to be descendants of Red Rackham, and is nearly mistaken as one of them. Thankfully for all, clearer logic prevails and his first of many inventions we see in the series, the shark-shaped submarine, is first proposed, and then employed to great use. He soon moves in with Tintin and Captain Haddock into Marlinspike Hall (or "Moulinsart" in French), inherited by the Captain in the "Red Rackham's Treasure" book. (While this book was also adapted for the recent movie's storyline, Professor Calculus was mysteriously written out of the storyline.) Other characters appear recurringly without necessarily being main characters. The most important amongst these are Interpol's police officers Thomson and Thompson (identical in appearance but completely unrelated, and known as "Dupont et Dupond" in French), and Marlinspike Hall's resident butler Nestor (maintaining the same name in both French and English).
There are a total of 24 titles published in the comic series "The Adventures of Tintin," created by Belgian cartoonist Hergé. The series features the adventures of the young Belgian reporter Tintin along with his loyal dog Snowy. It has been widely acclaimed for its storytelling and artwork.