At one point in time we all hear it. For writers its through the words of a book that grips us and won't let go. One author changes our whole world and molds our future. Thanks to them we know that we must write. Some of us recieve the calling at a very young age, some a bit later. Depending on who we heard the call from, it gives our writing a certain tune. My writing is often fast paced with a lot of action and adventure. It isn't hard for me to discern where that came from.
A co-worker of mine joked that since I was a sci-fi/fantasy writer I didn't have much of a literary background. I was appalled and contemplated seriously wounding him, or at least throwing a stapler at him. But instead I stopped and thought about all the books I'd read in my youth. It made me think back to the author who's words called out to me and showed me my future. For me it was Robert E. Howard, the creator of Conan and Red Sonja. The first Conan book I read sucked me into a world that I never wanted to leave. I voraciously read every piece of his work I could get my hands on. Because he was my first, my writing definately has a spice similar to his, as you'll find yours probably has something in common with your mentor. There were others that strengthened the call for me. I found Frank Herbert and though I was confused by him at a young age, I was also intrigued. Margaret Wies & Tracy Hickman's Dragonlance series sealed the deal and made me realize there wasn't anything else in the world I wanted to do besides write fantasy.
Then teachers intervened and I was forced to branch out to Shakespere, George Orwell, and Mark Twain. In a way these great writers affect the calling of all writers because most of us have no choice but to read them, which is a good thing because they're brilliant.
Take a look at who you first heard the calling from, think about whether or not they've affected your writing style. Do you write the same genre as they do? It may surprise you.