With heart, humor, and heaps of adventure, 'Gravity Falls' captures the feeling of childhood summer vacation.

10 years ago, the animated series 'Gravity Falls' burst on to the scene with healthy doses of irreverence and Jewish mysticism.

Written by series creator Alex Hirsch, The Book of Bill is a humorous tie-in that reveals more about Gravity Falls and the mysterious Bill Cipher.

Alex Hirsch talks about Bill Cipher, Summerween, Gravity Falls, and which character deserves a 50 Shades of Gray-style spinoff. The Book of Bill is out now.