His Dark Materials by Philip Pullman series

His Dark Materials is an epic fantasy book series written by the famous British writer Philip Pullman. The first novel of the trilogy Northern Lights was published in 1995 (it was presented as The Golden Compass in some countries). It was followed by The Subtle Knife in 1997 and The Amber Spyglass in 2000.
The book series revolves around two young children Lyra Belacqua and Will Pary who travel between different universes in order to learn about their past and their future.
The trilogy begins with the story of Lyra and her animal companion Pantalaimon from the parallel world where they are looking for their kidnapped friend. Their adventures concern the plot around kidnapped children and the dangerous trip to the North Pole.
The sequel follows Lyra’s adventures in a fictional city Cittagazze. Now she is accompanied by Will Pary from our modern version of Oxford. He has a mysterious knife that enables main characters to destroy windows between different universes.
In the third installment the plot is focused on the past of Lyra’s family and her destiny and the war between Asriel’s army and the army of Authority. Lord Asriel is preparing the army to fight with the powerful Magisterium the theocratic authority which sends an assassin to kill Lyra. In the end, Lyra and Will break all windows between parallel worlds and they should forever stay in the world they used to live. They promised each other to sit at the bench in their respective Oxford Botanic Garden and think about each other.
This book series is considered as one of the most successful British trilogies as more than 17 million copies was sold worldwide. Also the film The Golden Compass was loosely based on this series involving such famous actors as Eva Green, Nicole Kidman and Daniel Craig. The film was released in 2007 and took more than 230 million pounds all over the world.
The trilogy won a lot of awards including the Carnegie of Carnegies, the Award from the Swedish Arts Council, the Astrid Lindgren Memorial Award.
Although this series is regarded as on the most favorable books for children it is often criticized by various religious organizations for its unconventional approach to the Christianity.
On the whole the trilogy is famous for its exciting adventures of main characters in the world of magic, mysterious creatures and universes that are too distinct from each other.