This might seem like an obvious choice. I’ve read many great series, but none of them compare to my Holy Grail of a book series.
Harry freaking Potter, written by the ever brilliant and tricky J.K. Rowling. Rowling instilled in me a love of reading that no other books could ever have done. I grew up with the books. Made friends because of them. They altered my life for the better. Say what you want, but Harry Potter will always be the bomb dot com.